For me, what started happening today was that YT videos would not play in a normal window, where I was signed in, but would play in a private window., where I was not signed in. When I went back to the normal window and signed out, videos would play, but after I signed back in, they wouldn't play until after I disabled ad blocking for YT.
In the end, YT videos will play in a window where I'm signed in, if I bypass ad blocking for YT, but the same videos will play in a private window or as embeds, even if ad blocking is enabled for YT. ARGH!