Network Testing - Using Separate Processes = Lag

Testing stuff in UE4 in a simulated network environment has always been one of my biggest issues, a while ago me and a friend was working on a bomber man inspired game which is currently on hold - and I had a metric tonne of problems trying to find a setup in the editor where I could test stuff and get an identical effect with a packaged project over Steam*(stuff that replicated when testing in the editor would not replicate in the same way in a packaged project)*.

Currently what I’m doing is unticking Use Single Process, and having Editor Multiplayer Mode set as Play as Listen Server, because to me this seem like the most logical setup*(I host a game via Steam, my friends join me - I act as listen server)*.

However now the issue is that when I’m doing this the client not currently having focus will be updating extremely slowly*( video)*.

Any ideas as to what I’m doing wrong? Or is this simply another part of UE4 that isn’t quite finished yet?