I don’t know if you realised but they changed they way you need to join friends. I don’t know if this will solve your issue though. You don’t need upnp enabled anymore, I don’t think, you just need to open ports 3074. After that you go into custom games, invite your friend and then they double click your name in the overlay. You should be able to start match like usual, with both players already on the same lobby.
undefined