Conversations involving multiple participants, allowing collaboration and information sharing in Teams
I have been experiencing this daily and while closing Teams from the systems tray and re-launching it works, it's a really annoying bug. Haven't tried to clear the cache yet, but will be trying that for a more permanent fix. I am going to rename %AppData%\Microsoft\Teams\Cache to Cache.old and try that out for a few days.
Update: Closing Teams completely out and clearing the cache seemed to work. I will update if it happens again.