Plex Home Theatre full screen much bigger than the actual screen on MacBook.

I have Plex server on a different machine, just want to run PHT on a MacBook. When I first installed it, it worked fine. Then after a few sessions the full screen "\" toggle was suddenly much bigger than the screen - maybe a third missing from all the way round. Full screen of other apps was OK (VLC, Browsers etc). I messed with preferences for an hour or two but couldn't get it to work. So I fully uninstalled and then reinstalled - and it was working again. For about a day until suddenly happened again. RIght now I cant get it back to full screen to match my screen. I just reinstalled again but this time it didnt fix it. Running it out to TV has the same issue - most of full screen off the screen.
In preferences the VIDEO option is greyed out - not sure if that is a problem as well. Basically not seeing a pattern here..appreciate any suggestions...