Xbox (and possibly PS?) players are not able to join their friends’ games. You go to invite and select their name but it simply says “unable to send invite please try again later”.
Dozens of posts saying this on reddit and jsp (surprised there’s not more…) but haven’t heard any mention of the bug here. I know it’s a beta but it leaves a terrible taste in your mouth when it’s been out for 8 and a half hours with no official word on this issue.