I use LibreTube and it looks like half of the instances keep getting shut down and then get back up, and the speeds for all are atrociously slow that it is just better to watch it on YouTube on Firefox. I heard a while ago YouTube was blocking certain Piped instances but do not know if that is the same case right now.
It seems like on Invidious, the default setting is to still have the end user load the video directly from YouTube, whereas Piped defaults to proxying the video through its server as well. I would imagine this makes Piped servers a lot more noticable to YouTube.