Issue #3 described above has been fixed in the latest versions of Teams in the app stores. Please comment if you are still seeing #1 or #2.
An error occurred while saving the commentJohn commented
Both #1 and #2 are present on two machines we have at our site. Quite a nuisance, since it's now impossible to clear the notification and I don't know when I actually have a new message and not a broken notification.