Attachments take ages to upload and view

We have an issue after upgrading our Rocket.Chat install to the latests, server / client and MongoDB (see versions below)

After upgrading, first to wiredTiger, then to version 4.2 / 4.4 then 5.0 all attachments added to chats i.e. images / audio / video etc take an inordinate amount of time.
Also clicking on these attachments also take an inordinate amount of time to show or start playing.
By inordinate I mean 3 - 5 minutes to show images or upload new attachments as oppose to just a few seconds previously.
None of our attachments are particularly large and affect ALL existing attachments (viewing) and new attachments (upload and or view)

The stack trace

I get the following stack traces in the Rocket.Chat logs which seems to indicate a missing parameter OR missing indexes. Any ideas how to fix this will be appreciated..

ufs: cannot read file "mC3nrWQ3cY7ifoJwz" (Executor error during find command :: caused by :: Sort exceeded memory limit of 104857600 bytes, but did not opt in to external sorting.) MongoError: Executor error during find command :: caused by :: Sort exceeded memory limit of 104857600 bytes, but did not opt in to external sorting.
at MessageStream.messageHandler (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/connection.js:272:20)
at MessageStream.emit (events.js:314:20)
at MessageStream.EventEmitter.emit (domain.js:483:12)
at processIncomingData (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/message_stream.js:144:12)
at MessageStream._write (/app/bundle/programs/server/npm/node_modules/meteor/npm-mongo/node_modules/mongodb/lib/cmap/message_stream.js:42:5)
at doWrite (_stream_writable.js:403:12)
at writeOrBuffer (_stream_writable.js:387:5)
at MessageStream.Writable.write (_stream_writable.js:318:11)
at Socket.ondata (_stream_readable.js:718:22)
at Socket.emit (events.js:314:20)
at Socket.EventEmitter.emit (domain.js:483:12)
at addChunk (_stream_readable.js:297:12)
at readableAddChunk (stream_readable.js:272:9)
at Socket.Readable.push (stream_readable.js:213:10)
at TCP.onStreamRead (internal/stream_base_commons.js:188:23)
at TCP.callbackTrampoline (internal/async_hooks.js:126:14) {
ok: 0,
code: 292,
codeName: 'QueryExceededMemoryLimitNoDiskUseAllowed',
'$clusterTime': {
clusterTime: Timestamp { bsontype: 'Timestamp', low: 2, high: 1642705737 },
signature: { hash: [Binary], keyId: 0 }
},
operationTime: Timestamp { bsontype: 'Timestamp', low: 2, high: 1642705737 }

Server Setup Information:

• Version of Rocket.Chat Server: 4.3.2
• Operating System: Ubuntu 20.04
• Deployment Method: Docker
• Number of Running Instances: 1
• DB Replicaset Oplog: --oplogSize 128 --replSet rs0 --storageEngine=wiredTiger (single instance replica set)
• NodeJS Version: v12.22.8
• MongoDB Version: 5.0.5
• Using GridFS for file storage

Client Setup Information

• Desktop App or Browser Version: Both
• Operating System: Multiple

Steve

Start by reproducing attachment upload and viewing with GridFS while inspecting the MongoDB query behind the ufs: cannot read file error and the MessageStream stack trace. Done means existing attachments load and new attachments upload or play promptly without the sort-memory error.