Linux version works well after following the instructions posted below however version number is 1.3315.
Linux fix to get lobbies working:
appid is 1782210 (put this text into steam_appid.txt in the root dir alongside the game executable)
grab libsteam_api.so from
https://github.com/rlabrecque/Steamworks.NET/releases/download/15.0.1/Steamworks...
(this goes to 'CrabGameLinux_Data/Plugins/')