promise to test port related issues could tonight
Ok OP. So we did make a port related test on ps3 with arkhne, fire and cap today, as promised. Ggs btw guys. Some of cap's ports were not open so he could not hear me on his mic but the others could. Also, he couldn't join my freshly established lobby, even if arkhne were inviting him from it ( but the invitation worked in arkhne's established lobby, though, the round before).
So the theory was that in the netcode, the lobbies' port addresses are established at setup time based on the hosts ports capability, and various ports are used simultaneously. And that is what we tested.
if a host migrated (ie by the previous host quitting) into that lobby, those "lobby" port settings might prohibit you from joining.this would also explain why you might join later, (when the host creates a lobby fresh). This mean that there are a mighty number of people that cannot "see" some lobbies out there and u might never meet them, unless through another host. (And even when, stuff like mics might be silent, even though both have it switched on).
My gut feel tells me that this is also related to the ingame joining memory leak, because for these cases the netcode drops a new player into the game without verifying that the players' ports are "compatible".
So the best way to fix most of these port issues is to open up the ports listed in my other post.
This would probably be true for xbox, pc and wii too.