Why Is my Apple Music album artworks missing after syncing?

So I recently upgraded both my Macbook Air M1 and my iPhone 14 (Sequoia 15.0.1 upgraded from Sonoma, and iOS 18.0.1 upgraded from 17)...and somewhere in the midst of it all a TON of artwork for my music library was completely messed up.

I did a fresh install on my iPhone and when I resynced my music, more than half of the artwork was completely missing. And it wasn't consistent--sometimes it would be an entire album missing, sometimes only a few tracks on an album were missing the artwork. The artwork showed in iTunes on my Macbook, but just wouldn't sync over.

I can fix the issue by downloading a new version of the artwork manually in iTunes, but that's cumbersome work. I don't like to have iTunes manage my artwork files automatically because it often gets the artwork wrong.

Anyone else having a similar issue? Any thoughts why this happened? Is there something in iOS 18 that is more picky about the kind of artwork file used with music?

Any help is appreciated. Thanks!

[Re-Titled by Moderator]