Thank you for reminding me. We have managed to solve the issue. It was related to the deactivated Setting "UsersPermissionToReadOtherUserEnabled" in our tenant Settings. We activated it via PowerShell and all usernames appeared correctly.
Active users in Microsoft Teams appear as "unkown user"
Tim Hölger
26
Reputation points
Since about three weeks the following problem has occured in our Microsoft Teams: Active users within our tenant appear in Microsoft Teams as "unkown user". This happens in the teams members list as well as in the activity feed. Clicking on such an user an starting a private chat shows the correct name. What's the reason for this behaviour and how can we fix it?