I have attached a video of what I seen it was like void but mobs were visible and only worked in that position as far as I know. I was standing on a block on a chunk boarder.
I have also attached a screen shot explaining in more detail than the video.
Sorry for the audio in the video.
Environment
Window 10 1809 build 17763.557
java version "1.8.0_201"
Duplicate of MC-63020