Wrong album artwork in Music and artwork not syncing

Over the last year or so, I have noticed my album artwork being replaced with wrong/random art. My music library is over 60GB, dating back to 2006, and features lots of compilation/special issue CDs. These CDs are long gone and I have now spent weeks tracking down images of the CD covers and manually downloading and changing back the artwork and checking "album is a compilation by various artists."

(I have noticed a pattern where compilation albums get split up and art has all been replaced with the album cover for the 1st track of the album or the artists' own album that featured the track).

I have turned off "automatically update album artwork" in Music preferences. Also note: I do NOT subscribe to Apple Music, just using the app fka iTunes. After this experience I can tell you I never will subscribe to this service.

I have spent a lot of time over the years curating this collection and now I don't even recognize it. It is is extremely frustrating. These were my CDs that I owned and ripped legally, why would Apple replace the art that came with the CDs? Rude.

My two questions:

Why is this happening?

Now that I have updated the art in my library on my MBP, some of the newly restored artwork is not syncing to my iPhone & iPod. But some has.. how can I fix this?

Thanks is advance!