Usernames instead of displayNames for random users

Description:

Steps to reproduce:

1. Install or update Rocket.Chat to version 4.3.1. Set display their full names instead of usernames.
2. Sync users with LDAP
3. Start chatting with people. Notice that some of them have their usernames instead of full names. But their full name is displayed correctly in the chat itself.

Expected behavior:

Display full name of users (their first name and last name) in the sidebar contact list and in chat header

Actual behavior:

Username (LDAP login) is displayed for random users in the sidebar contact list and in the header

Server Setup Information:

• Version of Rocket.Chat Server: 4.3.1 (but has been there since at least 3.18)
• Operating System: CentOS 7
• Deployment Method: tar
• Number of Running Instances: 3
• DB Replicaset Oplog: enabled
• NodeJS Version: v12.22.8
• MongoDB Version: 4.4.9

Client Setup Information

• Desktop App or Browser Version: Firefox 96.0.1 for instance (but is seen on any browser and latest app version)
• Operating System: macOS, Windows, Linux

Additional context

We've compared normal user accounts with ones that have that bug and seen no difference in db.users table.

Relevant logs:

There are no relevant logs.

Start by reproducing the issue with LDAP-synced users in Rocket.Chat 4.3.1, then compare the user data and rendering used by the sidebar contact list, chat header, and chat itself. Done means affected users consistently show their configured full names instead of LDAP usernames in the sidebar and header.