Im on 5.6.1 and using Advanced Sessions Plugin, OSS Steam and Steam Sockets and I get the same error (LogSteamSocketsAPI: Warning: SteamSockets API: Warning Ignoring P2P signal from ‘steamid:XXXXXX’, unknown remote connection #YYYYY) in server logs when my friend tries to join me.
Any update on the actual cause of the issue ? The error comes from Steam servers so its hard to debug it in UE code.
Edit: I forgot to add the “listen” param when my hosting player (listen server) opens my in game level