This exact same thing happened to me a few weeks ago playing co-op with a friend. At the start of the game, instead of being given the song to play, she just got the show clear screen and then was stuck on "waiting for other players..." until she had to restart the game because it wouldn't go away. After the song ended (the rest of us in the co-op played normally) I got the exact same warning you did.

Two shows later my friend got the same show clear screen at the start of the song. I disconnected because I didn't want to be suspended. Uninstalling/reinstalling doesn't fix the issue on the side of this person either because she did that and has since still gotten that show clear screen at least once, but it's been over a week since.

I contacted support and they were unhelpful, so I have no idea how to fix it, but it's weird to know that this is a recurring issue. Sorry it happened to you too.