My cousin, housemate and I are still having this issue. We had 3 Xbox 1's in our household on the same network, and have just added a 4th for my cousins fiance. We are all trying to play together. Sometimes 2 of us can join a fireteam, other times we can all get in, some times none of us can get in together, and the strange part is sometimes when 2 people are successful in joining (A+B) the third cannot (C) but then if B leaves, C can join A. And it just continues like this. We can temporarily fix the problem by restarting all xbox's completely, but this only works sometimes. I have an Asus AC88U router that is brand new, and I have a hard time believing that this router is having UPnP issues, especially when the Xbox's can all be on the network playing other games, browsing Netflix, etc without issues. I'm really hoping Bungie can at least be more transparent with this problem. Explain to us why it is taking so long to fix.