Xbox cloud gaming - ultimate subscription but games not working

Recently I have been unable to play games on Xbox cloud, using my iPad, Steam deck or Android phone. I have an ultimate subscription and am signed in (I have tried signing out, restarting and also using a device for the first time.) Symptoms seem to be described by others, too - only Fortnite lets me click "play" but that then says "we'll be right back". All other games, including those I've played before, have a darker 'play' button that doesn't respond when you press it. I've had this problem for over a week now.

Thanks

:)