All,
Recently Valve's been migrating games over to their new master server protocol and as a result, most of the servers for ZPS aren't visible on the Steam Server Browser. Server owners need to put these commands into their server.cfg (they've been confirmed to be working on both NMRiH and ZPS) THIS IS A SERVERSIDE FIX ONLY
sv_master_legacy_mode 0 // Disable legacy mode, since steam master servers won't support it anymore.
heartbeat // Send heartbeat that this server is ready. Should be the last line of the config.
Thread for this problem is located here