Getting strange pixelated lines over certain new release MKV files

[OCBeas]

Getting strange block lines of pink and green coloured pixels over certain h265 MKV files when playing back on a smart tv. Most play absolutely no problem, but a couple of new ones play with audio and picture fine but with the lines over the screen?

[Woodstock]

First thing to eliminate is bandwidth and decoder issues. Do you see the same pixelation when playing on something like VLC on your computer, with the file local to the computer?

h.265 uses a lot of cpu power to decode if your set doesn't have a hardware decoder. It could be a simple as your TV not being able to decode fast enough on high-motion or high-detail sequences.