I noticed the same issue 2 days ago, was still investigating myself. At first only a few URL's/video's would break at noembed.com's api and return 503, but others kept working fine. (You can test at https://noembed/com/demo .
Also in my case some recent vidoes but also older ones (> 2 yeers) from a customers channel would randomly break and others still worked. With one video there was even a variation in it if you use youtu.be or youtube.com in the request URL to the service :-S . But it seems to deteriorate now with more and more videos becoming unavailable.
I customised/extended the default embed tile with some styling options and I also did some rewrites on the url to youtube-nocookie.com.
But now that I'm debugging my code tile that does this it seems 100% broken because I was depending on a url key being returned in the json response from noembed.com. It's no longer there in the answer and it's also not in the oEmbed answer I get directly from Youtube's oembed api. But I have no clue if noembed was adding this before or if Youtube changed this and noembed was only passing it along.
Fortunately in my project this extended Embed tile was already relabeled to a 'youtube tile', so I don't need the provider choosing and will query https://www.youtube.com/ directly.
I remember reading somewhere in november or december that Youtube is planning on removing the https://www.youtube-nocookie.com option alltogether in the near future: take it with tracking/advertising cookies or host your video's somewhere else. :-/