When you say you couldn't join the lobbies each other created, do you mean you were unable to connect or were you experiencing crashes after a map finished loading?

Also, do either of you happen to have any mods downloaded/installed to your game? Some mods change things to games that are not compatible with another game if the person with a mod like that is the one hosting the server. For instance, if someone has downloaded a mod in which it adds a new weapon or equipment to a class or an entirely new class, that would cause a conflict between your two games. This is not the case however when joining other people's games with a mod like that installed (as long as the original content is intact, if vital) because the host's game is being used as a basis for what your client is receiving, at least generally. Mods that do not cause conflict are usually called client-sided mods because they only affect your client and because of that, you could join a host game and the content would still be enabled. An example of this would be almost all graphics mods.

No maps loaded. I got a 30 second busy screen, then an error message claiming I failed to enter the lobby. Same vice versa, consecutively. Nothing ever crashed.

I had mods installed before updating, but I uninstalled and deleted everything before installing the latest update, so no issue there. Friend has no mods on his Steam version.

The lobbies we tried to join together were just typical, unmodded libraries.

A few alternatives... you could try using the SWBFSpy master-server, which connects you to a different server list, separate from the one GOG/Steam uses. The advantages of doing that are having better general stability and having real dedicated servers, as well as a more accurate ping measurement like GameSpy had. Keep in mind you can always revert the changes and use the GOG/Steam master-server if desired, and that, the SWBFSpy service works for all game types including the disk/retail version of the game. The only disadvantage to using the SWBFSpy service/master-server comes through the lack of players, though that probably isn't an issue for you if you just want to play with your friend(s). I'll provide a guide at the end of the post if you're interested in doing so.

And of course, if you don't want to do that, you can always just spend the small 10 dollar fee (though I agree it is ridiculous that you have to do this in order to cross-play, seemingly) and be done with this mess.

Whatever you choose I wish you the best of luck with finding a suitable option. Hell, you could even wait for the GOG development team to potentially solve this issue themselves, but I am doubtful... Again, good luck.

http://steamcommunity.com/sharedfiles/filedetails/?id=693147305

Thanks! Hopefully the actual issue is resolved and we actually get what we paid for.