HEVC x265 media only works with subtitles enabled.

Hi,
Having a very annoying issue where if I play x265 content with subtitles disabled (none) the video either refuses to play (on android devices), plays but has a letterbox of pixelated mess making it unwatchable (on my samsung tv with plex app), or plays fine on an i7 machine.

All devices work as normal if I enable any .srt in playback as my server is powerful enough for any transcode:
i7 2600k 4.2Ghz
16GB RAM
can play 4 streams at once no issue

If I’m currently playing content on my phone but switch to no subtitles:

Same here. x265 only plays transcoded on my samsung. Direct play gives me the same pixelated mess.