So I know this is a pretty common topic on here, but I have tried every solution I've seen and cannot figure out what is wrong, so I want to detail everything that has happened so far in case something stands out as a glaring issue.

My friend, who is on Steam, and I, on GOG, tried to join a session made by another friend on Steam. The first time we were setting up the game, We were both able to join the lobby and make our characters. When the host pressed start game, the music cut out, and after nothing happened for 10 minutes, the two of us who joined crashed, while the host loaded in.

We tried again, both connected to the lobby, got our characters assigned, pressed start, and the music cut out. This time, the other Steam friend joins, and only my game crashes. This is when I decided to try many of the troubleshooting solutions detailed on many of the forums, from deleting the game, verifying files, verifying firewall permissions are set properly, and even downloading the game on Steam instead of GOG.

All this did was introduce a new issue on both Steam and GOG, where when I connect to the lobby, it is stuck on "waiting until the server can admit new players" and then kicking me saying "session has been terminated". All the while, the other Steam friend can now connect with no problem and join the game. I've even tried on an entirely separate computer, and the session terminated issue was still as far as I could get.

One thing I know is not the problem is my internet connection, as I can play any other multiplayer game with zero issues. It may be a router problem seeing as it happened on both computers, but I have no idea where to begin, especially after knowing that connecting to the lobby worked the first two times around.

If anyone knows anything about why this may be happening or other solutions, please help, and please feel free to repeat what others have already said for solutions as I may have missed a thing or two in trying to figure this out