I’m also getting this same problem on 4.18.0 on a project that used to work on UE 4.15. Apparently, this error arises because a chunk of code marked with “TODO: START TEMP FIX FOR UE-42508” (World.cpp - line 6419), as far as i could debug it, the netdriver was ok before this, and would be working if the temp fix hadn’t been applied. I’m not using steam subsystem, just trying to connect two machines through PIE.