Server blocking one player

Dear facepunchers,

I have a concern with my servers, as they seem to block out one specific player, making him unable to connect.
I have no clue anymore as to how to fix this from my side, and he has no clue as for his side, so I decided to try here.

The person in question has tried all basic things, like:

  • port forwarding,
  • reinstalling,
  • disabling steam cloud,
  • checking firewall
  • checking whether VAC isn’t blocked in a way
  • etc, etc.
    The thing is that he can connect to any other server. And he can connect to my servers with any other steam account from the same machine.
    He could also ping my servers through commandline, yet whenever he tries to connect the ‘connection failed after 4 retries’ message appears, and when looking at the game info of friends on the same server it says ‘server not responding’.

From my side, he is not banned, his IP is not blocked in my VPS, etc. I have checked subnets, possible Steam ID blocks, etc, but I’ve come up with nothing at all.
He is the only player with whom I’ve had this problem (as far as players have reported to me, that is).
I do not get any message of attempt to connect in my server’s consoles, or any feedback from the server.
It is as if my server reads his SteamID, and immediately refuses connection, as if there never was a connection in the first place.
I have three different servers hosted, on three different IP’s, but all on one VPS, the third one I freshly installed today, and still he can’t connect.

Is there anyone here that could possibly shed some light on how this is possible or even how I could fix it, so that this player can finally enjoy playing on my servers again? Because I am completely clueless.