To me, and to many other customers, often it happens that Teams on Windows is unable to receive messages, while they continue to arrive on mobile apps.

I have found that the solution to this problem is to clear the Teams cache.

For Windows:

On the top right corner, log out from Teams:
Teams_logout

Then use File Explorer to go to %appdata%\Microsoft:
Teams_navigate

And finally delete the Teams folder:
Teams_delete

Now you can restart the Teams app.

For Mac:

On the top right corner, log out from Teams:
Teams_logout2

The use Finder to navigate to ~/Library/Application Support/Microsoft:
Teams_navigate2

And finally delete the Teams folder:
Teams_delete2

Now you can restart the Teams app.