Some YouTube videos not playing

I've been having this weird issue that I blamed on BTTV extension, but apparently it's not.

Some YouTube videos don't play when I click the play button, it shows the spinner, I see some /videoplayback requests, but the button remains in place and nothing actually plays.

Tests done so far:

• It does work in Private mode (even with uBlock), but not in normal mode.
• Disabling extensions or clearing cookies doesn't help.
• The issue resolves by itself after a couple of hours and I don't see any meaningful differences between working and broken videos.

The most recent examples are:

• https://www.youtube.com/watch?v=k86UdUN6YlA
• https://www.youtube.com/watch?v=MjYSeT-T5uk

Any advice?

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Edit: resolved by itself sometime in mid-July.