I’m on Xbox One, and neither my friend or I can connect to a multiplayer session.
Edit: I can join games, he can’t.
I too have this same issue. My brother and I who live in separate locations (so not on the same network), will try joining each other, and it will say joining host, and then kick us back to the title screen, unable to join. Our NATs are open, we have tried joining each other through xbox party, friends list, game invite, same sequence of events. We are both able to join random games however. We have both tried resetting the XB1s, as well as routers.
How can we spend time with each other now 
Hard Console Restart fixed this issue on my Scorpio.
I have tried that as well, sadly no resolution.
Hello all,
I am having this issue on Xbox right now I can not join any MP session be it friends or random. I get a loud buzzing noise then kicked back to the Xbox home screen, During my stream last night two others said they are having the same issue. It starts to load world then boom out.
SPP