Microsoft have identified a recent change that appears to be the source of a number of issues affecting Office 365 and MS Teams.
They are in the process of rolling back the change to mitigate impact. Please follow http://status.office.com for updates on this issue.
Microsoft have now reverted their update and systems appear stable. Some M.io customers may have been prompted to reauthenticate their service account. Please complete the instructions provided, or contact M.io support for further assistance.