I have this problem happening to me from time to time, and quite randomly with no real reason why. Usually, it happens on a new user profile installation with a new updated Teams app.

Closing down the app and reopening it wouldn’t help, nor did reinstall it. The only way around it, at least I found, is to close the app, and remove all the files related to the Teams app in the user profile folder. And then reinstall it.

%userprofile%\appdata\local\Microsoft\Teams
%appdata%\Microsoft\Teams

The first folder is the app folder and the second one stores all the user data.

Once all is cleaned up, reinstalling the Teams app and it should be all good to go.