(I did some more testing and I cannot see the strips if lookahead-slices was disabled (vertical resolution less than 720).) EDIT: tested with existing encodes - couldn't replicate this with the latest x265 using the same source.
This is how it looks on the TV and on my display, a snippet from the upper left corner (seriously exaggerated by getting the brightness real high):
https://imgur.com/a/gO45OYB
I recall seeing this also with x264 encoded videos. Different decoders have been used, on the computer it's the NVIDIA GPU and on the TV it's whatever is on Apple TV 4K - VideoToolBox I think.
EDIT: this older clip shows the thing at the start, turn up the brightness to see it:
https://drive.google.com/open?id=1ui...b7A0ob9nqtJKa2