Xbox Live (Mobile) Multiplayer

I can join any of my friends currently on Xbox Live other than one. We were able to play for months together before this problem arose. It’s been going on over a month now. We can join through mutual friends, but whennjt is just us we are seen as offline
and invites to games do not go through. Both of us are on mobile devices, and have this problem no matter what internet we are on. I know we both do not have the setting “appear offline” chosen because both os us can connect with other friends. I’ve gone through
all the xbox support pages and nothing is giving me answers. Any help would be appreciated

:)