Microsoft has reported that they are investigating issues with Teams.
Title: Can’t access Teams
User Impact: Users may be unable to access Microsoft Teams.
More info: Users able to access Microsoft Teams may experience degraded performance with multiple features.
Current status: We’re analyzing system telemetry to isolate the source for the issue. In parallel, we’re reviewing recent changes made to the service as a potential root cause.
Scope of impact: Initial indications suggest that any user could be affected by this issue.
The issue has been fixed. It may still be required to restart Teams application.