My Mi Box is connected to an old 1366x768 pixels HDTV and I noticed some 4K videos or some 4k HDR videos won't play normal on Youtube, they buffer a lot and the audio is twice or more the speed, they sound accelerated, this always happen with a free short movie I got from google play movies called "Sintel", which also appears on my youtube library as a 4K video, I also tested other 4K videos, some of them play normal but others don't.
This is an example of a video that won't play normal: https://www.youtube.com/watch?v=MuAmv2PsqEw
Obviously the videos won't play in 4K but according to statistics they play at a maximum resolution of 1080p/24, 1080p/30 or 1080p/60 depending on the video.
Do you have the same issue?
Just tested the video you provided on my Mi Box, latest OTA and latest version of YouTube, connected to a 1080p TV. It buffers a lot, and it's something that usually doesn't happen when the video is streaming at 1080p, and audio is messed up really bad, so I guess it's not just your problem.