Yes, this is a bug that has been fixed & reintroduced.
I made a post about it yesterday. In that post I linked to one from last year that gives fixes. But as you can see from my experience they don't always work. Just keep deleting save data, restarting and trying to open your game. If you log out, you can't play any other game or go to other apps without restarting again.
As the login issues from this time period are now resolved, we have decided to close the thread. If you need further assistance, please go ahead and start a new thread in Xbox Support.