Have you read past that screenshot of the code, though? It says the problem was not limited to Firefox, it seems Edge users reported problems as well. Anecdotally, I did experience that delay problem on Thorium this weekend as well. I have seen a variation of this problem almost a month ago, where sometimes the video would take a long time (like, over a minute, sometimes) to load, or often just not load at all. So I just chalked it up to Youtube having done something stupid on their end.