I can join any hosted game and connect with all players. My port is fixed and everything works like it should.
Haven't had a single problem connecting with any individual player when I join another host.
When I myself try to host a game, other players can't join my lobby at all.
They get a message along the lines of "Can't connect to host".
I notice I have 2 choices for my Online IP in the options menu, don't know if this affects anything?
Like I said I don't think the problem has anything to do with the Port FW, as it works perfectly during any other lobby I join.