Hi, this issue has been fixed for me.
I tried clearing caches, adjusting Content Filtering and components but nothing worked. After clearing the caches for YouTube/Google, I logged back into YouTube and noticed a box shows that only my main account remained on YouTube (screenshot 1) but all other accounts were logged out. Somehow, my main account was still active on YouTube, so the issue kept happening.
I had to manually log out of YouTube and log back in (screenshot 2), and surprisingly, that fixed it. Now I can watch videos normally.
