There are 2 other threads about this in the section of the site, but I'll summarize it. Basically, YouTube is doing another purge, and even targeted the official channel run by BP. This purge includes people who release smaller sections of content (like songs from the new series), or review content. Major fandom YouTubers saw their channels taken down, it's only time before the minor ones go down.
I stopped accessing Chipmunks content via YouTube after the 2011/12 purge, which left little high quality stuff left, but it's possible that there may have been other purges in between.
I'd recommend you look at those other threads to get a general idea.