After Effects starting to act and look weird..

Since a couple of weeks now my After Effects CC 2018 is acting up a bit. When I do a pre-render, all graphics disappear and are replaced by a dark grey background except for the actual render window. Since I can't access my play and pause button at this point I use the spacebar to stop and play the pre-render. When I press the space bar everything goes back to normal. (Image 1)

Also, the AE work area is starting to creep out of the boundaries of my computer screen. Have I managed to touch some kind of quick command? (Image 2 -not very clear, perhaps.)

I use an iMac which still runs on macOS High Sierra 10.13.6.

Any help is greatly appreciated.