According to data from DownDetector, issues began at roughly 7am ET/12pm BST, preventing users from joining calls. Given the early time, users in Europe and Asia were first to report issues, but the outage appears to be affecting Microsoft Teams customers on the East Coast of the US now as well.
The Microsoft status portal is currently reporting no issues for Teams, so the source of the problems is unclear.
However the official @MicrosoftTeams account has confirmed that “our team is investigating an issue with Microsoft Teams”.
It seems that Teams for Buiness, Teams Personal and Education users are all affected, with some users complaining they had been kicked out of active calls, and others suffering an Error 401 message.
Microsoft has been advising users to open support tickets and follow its admin center for further updates.
We’ll update this page as new information emerges…