[2023] 24/7 server, unresponsive after only a little while

I don't play this game so forgive a naive question - when you say run a server, you mean starting a CK3 MP have as a host, and just letting it run without the host actually playing, something like that?

As to your problem, your idea of switching the new machine to the old location is a good one - that will determine if it is in the machine, or the ISP/modem.

My guess would be some sort of hibernation or power saving mode.  

AndrewT said: you mean starting a CK3 MP have as a host, and just letting it run without the host actually playing, something like that?

That's what it sounds like. Never heard of anyone doing that before.  

If you have a VPN, connect via that before you start the server. That will take any firewalls out of the equation.