Debian Dedicated Server - No one can connect except me (Ports are open)

Im hosting a gmod server on a vserver on debian but somehow I am the only one who can connect.

The server is fresh installed, no addons sv_lan is 0, no errors in the console, it says “Connection to Steam servers successful.”. No one can connect they dont receive any answers from the server if they connect. The strange thing is with my internet connection i can connect without any problems but nothing is hosted on my machine everything is running on a dedicated server with public ip. If i use vpn i also can’t connect.
Sometimes a random player can connect to the server but my friends can’t.

The same problem happens if i host a csgo server no one can connect except me.

Other servers like Ts3 are working fine. I also testet the necessary ports with a minecraft server, no problems. I reinstalled Debian and also tried an older version but nothing helped. I think it has something to do with the steam servers or some kind of routing problem i don’t know…