Intermittenly unable to find server in steam

I’m currently using SteamSubsystem for our packaged build. I find it that we’re randomly unable to find each other’s game. No particular pattern that we know of. No logs , it’s just being no server found although it’s been hosted. The weird thing is that without online subsystem, the game has always connected at a 100% rate if port forwarding is done.

  1. is there a way to debug the process of finding server? what are the processes involved?

  2. what are the known issues where steam isn’t being able to find servers?