I have had this issue with Qobuz:
The reason turned out to be, when a label or an artist makes a change on an album in Qobuz, Qobuz flags the existing copy as unavailable and uploads a new copy.
Over the course of a year, it was pretty brutal and a ridiculous number of my albums suffered from this rot. It was then compounded by some odd issue with Qobuz where it will just remove the albums from your Roon library but you can still see them in Qobuz (although they are marked as unavailable to play).