Hosting a legacy CS:GO dedicated server, how are community servers handling MasterRequestRestart?

I've been trying to get a CS:GO legacy dedicated server running on Linux. The server starts up fine map loads, ports bind, GSLT login works, VAC activates but once it connects to Steam, the Game Coordinator sends MasterRequestRestart which silently disables the networking layer. The server process stays alive but stops responding to any packets, including player connections and queries.

There are clearly still active CS:GO community servers out there (visible on tsarvar and gametracker with real players on the same 1.38.8.1 build), so someone has figured this out.

Things I've tried that didn't work:

- Spoofing version numbers in steam.inf

- Running with -insecure (forces LAN-only without GSLT)

- Blocking Steam IPs via iptables (falls back to LAN-only)

- NoLobbyReservation SourceMod plugin (binary signatures don't match this build)

Has anyone here had success getting a legacy server running, or knows what approach the existing community servers are using? Any pointers appreciated.