Is it possible you have more than one artist listed as Moby in your database? My Moby albums are all showing correctly (I only have 8 albums, but they’re all there) but I have had situations where albums were split between two artists with (possibly) identical names. It might be worth checking that this isn’t happening in your case. If it is, merge the artists.
remove all your Moby albums from your storage location.
clean up your library (Preferences -> Library -> Library Maintenance -> Clean up library).
Re-add the albums to Roon.
The reason I suggest this is because I’ve had issues with mis-identified albums where no amount of tinkering with the metadata made any difference - the erroneous info seemed impossible to correct - but starting over with exactly the same album seemed to fix the problem. You may have already tried this.
I might be misunderstanding you, but that sounds like much the same structure I use (source disk/M/Moby/albums). If so, all you’d need to do is copy the Moby folder to another location, clean/rebuild the database, then add the folder back into its original location.
I have Moby from CDs, bandcamp, HDTracks, Qobuz, Onkyo, himself. That’s what I mean. My directory structure starts with the source (CD, , etc) so for example all purchases from HDTracks are under that directory, all ripped CDs are under CD, all ripped SACD are under that, etc. I have about 20 sources total.