Well if I'm not mistaken Hamachi is supposed to mimic a LAN server sort setup. With a LAN server you don't need to do things like forward ports, so if there's a problem when running without Hamachi, then I guess it would be an indicator of the router problem or more specifically something to do with port forwarding. Just a guess though. Idk when I have problems with port forwarding it usually just doesn't allow me to host not something like this. but either way its an early multiplayer version of an early access game so its fine it will eventually be fixed and its the only bug I have found. anyway hope it gets fixed soon for others since the multiplayer is amazing.