Seems like Piped and Invidious are both on their last legs. Public instances on both services are pretty iffy, they go down fairly often now. Freetube works well on desktop but no real way to sync subscriptions and watch history to a phone. Self-hosting Piped/Invidious might be the solution but I don’t know if it’s worth the upkeep when YouTube is actively fighting against it.
NewPipe has worked pretty reliably for me throughout all that. I did notice LibreTube required switching instances a lot more often (which is actually why I switched back to NewPipe).
Hopefully, they’ll be able to keep things working. If not, YouTube’s never been much more than a fun novelty to me, so I wouldn’t miss it too much.