Generally I never had problems across a home network of PC's.
Your game server will use your Internet IP for others to connect on, you'll have that Internet port open so players can.
The game server will have an address of 127.0.0.1 of it's own and probably an internal network address as well of 192.168.x.x depending how you have that setup at home.
The PC your on will also have an address of 127.0.0.1 so using that won't usually work, you'll need to find out the 192.168.x.x of your game server on your internal home network. That can be found in the details for the adapter...
View attachment 6667
This PC would be 192.168.1.67
Only thing I can think of is maybe a firewall setting on the game server PC to allow connections via 192.168.x.x