It's absolutely not all, I'm an extremely casual listener, not 'into' music or anything, and I have plenty in a playlist that have disappeared (mostly I don't even know what they are, it's just greyed out with no information) for whatever reason. And that's just the stuff that was there at some point that I liked.

One of them has come back recently. It's still listed as by the wrong artist (same name, but dead, vs. the active artist who actually performed it) but I'm not reporting it again because I suspect I may have made it disappear for a couple of years in doing so before.

It's kind of crap and disorganised after anything more than barely glancing at it really, must be infuriating for (or just not used by) people who actually are into it.