I've read the "Content Missing" articlebut it doesn't completely answer my question, so:
A specific artist I was following went missing, which I understand, based on that article. When I say missing, I mean unplayable, it's still listed on spotify.
However, Spotify has an "alternate" version of this artist, represented under a different label, with most, but not all its albums. Other music services have this album. Could it be that Spotify hasn't gotten to it yet, or failed to add this particular album?