Today a user we'll call user 1 complained that since a few days or so he has to use the web app because his desktop client wont login. I go to his computer to check. The login prompt just closes itself after entering his username. I test if I can log in with my user on his computer: success. I check again if his account works: Teams just closes after entering his username. I reinstall Teams, same behavior. I delete the Teams cache folders in %AppData% plus all user credentials within the Windows Credential Manager. Nothing changed. Web app login still works fine for him.
Now comes the best part: User 1 goes to user 2's computer and logs out user 2. He then tries to log into user 2's Teams desktop client.
Same behavior. Microsoft Teams just closes after user 1 entered his username.
User 2 wants to log into his Team desktop client again.
User 2 now faces the same issue on his computer.
Microsoft Teams just closes for him.
User 1 infected user 2's workstation with this login bug.
User 1 and 2 are now forced to use the web app and are afraid to log into their teams accounts on other domain computers.