We also have problem making a 3+-player game.

We have had a 5 player game up and running through versions 11.2 - 11.4 but patch to 11.5 we just can't seem to get it to work.
We have tried all the usual shenanigans.

* Port forwarded,
* All running cable ( no routers)
* Hamachii / evolve
* x64 ...