Dedicated Server connection problem

[Viilea]

I'm hosting a server by a PC, normally, everything is configured and the server is good to go. Firewall inbound and outbound rules are made, router ports are opened, sandbox configs done, and the server is up and running.

For a while, it stays normally open, it even shows on the Archspace list, even the integrated list on the game. Suddenly, after a few minutes (sometimes, seconds) the server doesn't show on any list, no one can connect even via direct IP, and it stays running normally, and even the players that managed to connect before that, continue to play normally, no lag spikes, nothing. I've checked the router configurations, the firewall, anti-viruses are disabled, all the game configs are normal, and I don't have any idea of what could be causing this. The server specs are quite good, so I doubt its the matter.

 

Please, someone help me, I've spent my whole day trying to fix this and nothing worked.