LDAP import of users fails "Cannot read property 'replace' of undefined"

I having a working server with about 450 users... but one or two new users will not import from LDAP and why I try to import while watching the logs I get the following error:

rocketchat[30634]: Exception in callback of async function: TypeError: Cannot read property 'replace' of undefined
rocketchat[30634]:     at module.exports (/opt/Rocket.Chat/programs/server/npm/node_modules/limax/lib/limax.js:18:15)
rocketchat[30634]:     at slug (app/ldap/server/sync.js:23:9)
rocketchat[30634]:     at ldapUsers.forEach.ldapUser (app/ldap/server/sync.js:307:16)
rocketchat[30634]:     at Array.forEach (<anonymous>)
rocketchat[30634]:     at ldap.searchUsersSync.Meteor.bindEnvironment (app/ldap/server/sync.js:294:13)
rocketchat[30634]:     at runWithEnvironment (packages/meteor.js:1356:24)

The server is running on Ubuntu and has the following versions:

rocketchat[30634]: +------------------------------------------------------------+
rocketchat[30634]: |                       SERVER RUNNING                       |
rocketchat[30634]: +------------------------------------------------------------+
rocketchat[30634]: |                                                            |
rocketchat[30634]: |  Rocket.Chat Version: 1.1.2                                |
rocketchat[30634]: |       NodeJS Version: 8.11.3 - x64                         |
rocketchat[30634]: |      MongoDB Version: 3.4.21                               |
rocketchat[30634]: |       MongoDB Engine: mmapv1                               |
rocketchat[30634]: |             Platform: linux                                |
rocketchat[30634]: |         Process Port: 3000                                 |
rocketchat[30634]: |             Site URL: https://rocketchat.xxxxxxxxxxxx.com  |
rocketchat[30634]: |     ReplicaSet OpLog: Enabled                              |
rocketchat[30634]: |          Commit Hash: aece97e1a0                           |
rocketchat[30634]: |        Commit Branch: HEAD                                 |
rocketchat[30634]: |                                                            |
rocketchat[30634]: +------------------------------------------------------------+

This is syncing against a Windows 2008 R2 Active Directory server. Any ideas on what can be done to troubleshoot more and find out why my LDAP sync is failing all the time now?

Start with the stack trace in app/ldap/server/sync.js, especially the slug call at line 23 and LDAP user processing around lines 294-307. Reproduce an import involving the affected users and inspect which value reaches limax before replace is called. Done means LDAP imports complete without this TypeError and the cause of the missing value is addressed.