In regard to albums with missing tracks: at least for some classical music labels, it appears that they release "sampler" or "mini" versions of the albums that might contain only one or a few tracks. I suspect (but cannot prove) that these releases are for promotional purposes.
The good news is that in most cases the label also releases the full album to Qobuz. Confusingly, the partial album and the full album have exactly the same info: same title, same artists, same cover art, same everything except for the number of tracks. So if you search for, say, "Chopin Etudes Smith", the first item returned might be an album of Chopin etudes played by a pianist named Smith -- but it could be the promo version with, say, four tracks out of the expected 24. If that happens, keep looking! It will look like there are two listings for that same album, but one will be the partial version and one is the full version.
Frustrating? Yes. But easy to work around. And I think it's more the label's fault rather than Qobuz: Qobuz is just taking whatever the label sends them. Why the label sends the partial version when they also are sending the full version is a mystery, but whatever.....