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:

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

And finally delete the Teams folder:

Now you can restart the Teams app.

For Mac:

On the top right corner, log out from Teams:

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

And finally delete the Teams folder:

Now you can restart the Teams app.