Apple Music CD library splitting and artwork disappearing on external drive

Each day I rip a bunch of cds to my external drive (this is a 4tb G thunderbolt drive) as my iMac only has a 500gb internal. When I leave it at the end of each day, all my cds are organised in the library with artwork. I have a number of Opera sets that have 4 ads in each and it takes some organising to have them in one library folder with all the correct settings.

When I leave it switch it off overnight and then return to it the next day, all my opera sets are split up again into separate library cds and some have artwork missing. It's incredibly frustrating and all my work is undone. DO I need to check I have the correct settings somewhere? Should I consolidate my library? I'm stuck on it and can't figure out if I'm doing something wrong, or if my method is incorrect. Completely confused.

[Re-Titled by Moderator]

Original Title: What is happening to my cd library in Apple Music? - Strange, confusing and frustrating