Android sign in issues
This has happened three times, and I think it's related to either updating the Teams app, or installing/updating other Microsoft apps.
The issue is simple, at the sign in screen it simply says "we're having trouble signing you in". No other details, or errors (frustrating).
The only fix is to uninstall -all- Microsoft apps. I'm guessing this must clean up some shared authentication token data or something.
If you do some searching on Google, it's a rather systemic issue.