@sam_nazarko
The video glitch reported above did not occur under 4.9. The only thing I noticed was that my TV didn’t switch to HDR mode even thought the video description suggested it was HDR content. I think this is an established issue though.
We do still need to use the “double_write_mode fix” in order for Hyperion to grab the colours correctly with 4K content.
This shouldn’t be the case.
I suggest bringing up more details in Testing in chat.
Not switching the TV into HDR mode when playing HDR VP9.2 content is definitely a known issue. (Unless it’s been fixed very recently).
Covered in chat now.
Are there any news regarding this, or can I follow the investigation somewhere else? 
From what I can see, others can play 4K YouTube without issue. Some logs may give some clues why you are experiencing a problem.
Hi Sam, I posted logs earlier, but they are available here, let me know if there is anything I can test/enable or otherwise provide that would assist.
Unfortunately these aren’t debug logs, so it is hard to advise.
Please enable debug logging under Settings -> Logging, reboot, and reproduce the problem.
Right, will do a new test later today and get back to you with new logs!
@sam_nazarko Here are the logs from a new test, with debugging enabled. Hope this can shed some light on it.
These aren’t complete logs.
Please upload logs via the My OSMC system.