Hacker detected on Xbox

Apologies if this has already been asked but I couldn't find anything.

I have a friend playing on Xbox Series X. Whenever I join his lobby, his name is BAD USER NAME and his level is HACKER DETECTED. This has been happening every single game.

Once we start playing, everything seems to be ok? He gains XP and unlocks stuff like normal.

However, he is unable to join my lobby at all, it says he's been blocked. I double checked and I definitely did not block him.

He's never been banned from anything, nothing rude or sketchy in the user name. Restarting the game hasn't helped. Any suggestions? Thanks y'all!