Replies count correct but replies not visible after Slack import.

Importing a Slack export using Administration -> Import -> Import New File type Slack works.
The reply count in messages is correct but replies are invisible.

Server running on Ubuntu 20.04.3 LTS.
Deployed using snap install rocketchat-server --channel=3.x/stable

Server log:
I20211127-16:55:33.602(0) ➔ +-----------------------------------------+ I20211127-16:55:33.602(0) ➔ | SERVER RUNNING | I20211127-16:55:33.602(0) ➔ +-----------------------------------------+ I20211127-16:55:33.602(0) ➔ | | I20211127-16:55:33.603(0) ➔ | Rocket.Chat Version: 3.18.3 | I20211127-16:55:33.603(0) ➔ | NodeJS Version: 12.22.1 - x64 | I20211127-16:55:33.603(0) ➔ | MongoDB Version: 3.6.14 | I20211127-16:55:33.609(0) ➔ | MongoDB Engine: wiredTiger | I20211127-16:55:33.609(0) ➔ | Platform: linux | I20211127-16:55:33.609(0) ➔ | Process Port: 3000 | I20211127-16:55:33.610(0) ➔ | Site URL: http://localhost | I20211127-16:55:33.610(0) ➔ | ReplicaSet OpLog: Enabled | I20211127-16:55:33.610(0) ➔ | Commit Hash: 47eec58e6f | I20211127-16:55:33.610(0) ➔ | Commit Branch: HEAD | I20211127-16:55:33.610(0) ➔ | | I20211127-16:55:33.611(0) ➔ +-----------------------------------------+ I20211127-16:56:31.888(0) Unloaded the Apps Framework. I20211127-16:58:00.174(0) server.js:204 Slack Importer ➔ error TypeError: Cannot read property 'map' of undefined at SlackImporter._replaceSlackUserIds (app/importer-slack/server/importer.js:550:18) at SlackImporter.prepareChannelsFile (app/importer-slack/server/importer.js:44:17) at app/importer-slack/server/importer.js:210:28 at iterateEntries (/snap/rocketchat-server/1491/programs/server/npm/node_modules/adm-zip/zipFile.js:42:4) at Object.forEach (/snap/rocketchat-server/1491/programs/server/npm/node_modules/adm-zip/zipFile.js:150:5) at Object.forEach (/snap/rocketchat-server/1491/programs/server/npm/node_modules/adm-zip/adm-zip.js:425:16) at SlackImporter.prepareUsingLocalFile (app/importer-slack/server/importer.js:207:8) at MethodInvocation.getImportFileData (app/importer/server/methods/getImportFileData.js:66:37) at MethodInvocation.methodsMap. (app/lib/server/lib/debug.js:90:34) at maybeAuditArgumentChecks (packages/ddp-server/livedata_server.js:1771:12) at packages/ddp-server/livedata_server.js:1689:15 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/ddp-server/livedata_server.js:1687:36 at new Promise () at Server.applyAsync (packages/ddp-server/livedata_server.js:1686:12) at Server.apply (packages/ddp-server/livedata_server.js:1625:26) at Server.call (packages/ddp-server/livedata_server.js:1607:17) at DDPCommon.MethodInvocation. (app/api/server/v1/import.js:46:20) at packages/dispatch_run-as-user.js:211:14 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at Object.Meteor.runAsUser (packages/dispatch_run-as-user.js:210:33) at Object.get (app/api/server/v1/import.js:45:10) at app/api/server/api.js:400:82 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at Object._internalRouteActionHandler [as action] (app/api/server/api.js:400:39) at Route.share.Route.Route._callEndpoint (packages/nimble_restivus/lib/route.coffee:150:32) at packages/nimble_restivus/lib/route.coffee:59:33 at packages/simple_json-routes.js:98:9 I20211127-16:58:16.801(0) Missed import types: { group_archive: { type: 'message', subtype: 'group_archive', ts: '1620021987.002500', user: 'U01HPL15U6Q', text: 'hat den geschlossenen Channel archiviert', team: 'T01J4GQCAM6' }, tombstone: { type: 'message', subtype: 'tombstone', text: 'This message was deleted.', user: 'USLACKBOT', hidden: true, ts: '1618929565.006500', thread_ts: '1618929565.006500', reply_count: 3, reply_users_count: 3, latest_reply: '1618937423.011300', reply_users: [ 'U01UQ5ZDR6G', 'U01UM04FNBE', 'U01S2BQP4NA' ], is_locked: false, subscribed: false }, channel_convert_to_private: { type: 'message', subtype: 'channel_convert_to_private', ts: '1615273651.141600', user: 'U01HNTGP2J0', text: 'hat diesen Channel zu geschlossen geändert. Anzeige und Beitritt sind jetzt nur noch auf Einladung möglich.' }, sh_room_created: { type: 'message', subtype: 'sh_room_created', text: 'Started a https://xxx.com/call/R028QSK3TGS|call.', user: 'U01H6KE0407', channel: 'D0202GMP4AD', room: { id: 'R028QSK3TGS', name: null, media_server: '', created_by: 'U01H6KE0407', date_start: 1626859216, date_end: 1626859252, participants: [], participant_history: [Array], participants_camera_on: [], participants_camera_off: [], participants_screenshare_on: [], participants_screenshare_off: [], channels: [Array], is_dm_call: true, was_rejected: false, was_missed: false, was_accepted: true, has_ended: true, media_backend_type: 'free_willy', external_unique_id: '41a7b656-d12b-49a2-a5df-0b881e6a0706', app_id: 'A00', call_family: 'native_call' }, no_notifications: true, permalink: 'https://xxx.com/call/R028QSK3TGS', ts: '1626859218.000100' }, channel_archive: { type: 'message', subtype: 'channel_archive', ts: '1616733766.006100', user: 'U01HPL15U6Q', text: 'hat den Channel archiviert' } } I20211127-16:58:20.901(0) Setting default file store to GridFS I20211127-16:59:21.121(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:22.048(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:27.288(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:27.452(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:27.612(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:28.389(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:28.766(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:28.994(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:29.324(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:29.819(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:29.969(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:29.980(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:30.052(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:30.202(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:30.605(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:31.416(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:31.449(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:32.952(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:33.254(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:39.370(0) server.js:204 Slack Importer ➔ error Error: importer-message-mentioned-user-not-found at ImportDataConverter.convertMessageMentions (app/importer/server/classes/ImportDataConverter.ts:382:11) at app/importer/server/classes/ImportDataConverter.ts:456:41 at SynchronousCursor.forEach (packages/mongo/mongo_driver.js:1141:16) at Cursor. [as forEach] (packages/mongo/mongo_driver.js:920:44) at ImportDataConverter.convertMessages (app/importer/server/classes/ImportDataConverter.ts:430:12) at app/importer/server/classes/ImporterBase.js:204:20 at Meteor.EnvironmentVariable.EVp.withValue (packages/meteor.js🔢12) at packages/meteor.js:550:25 at runWithEnvironment (packages/meteor.js:1286:24) I20211127-16:59:41.622(0) Setting default file store to GridFS

Browser console:
TypeError: 'microphone' (value of 'name' member of PermissionDescriptor) is not a valid value for enumeration PermissionName.
e http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:971
f http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_withTemplateInstanceFunc http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
f http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
constructView http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
n http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
nonreactive http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:724
_fireCallbacks http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_withCurrentView http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_fireCallbacks http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_createView http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_materializeView http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
t http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_materializeDOM http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_materializeDOM http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
_materializeView http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
nonreactive http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:724
_materializeView http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
render http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
renderWithData http://localhost:3000/adba71143a63efa5332d24f595dbf70d16d46482.js?meteor_js_resource=true:768
l /client/views/room/components/BlazeTemplate.js:1

Start with app/importer-slack/server/importer.js at _replaceSlackUserIds and prepareChannelsFile, then inspect ImportDataConverter.ts at the reported mention-conversion errors. Reproduce the Slack import through Administration → Import → Import New File and trace how threaded messages are converted. Done means imported messages retain visible replies, not only the reply count.