Missing album art for some music files in Music on macOS Sequoia

Running Music 1.5.2.56 on macOS Sequoia 15.2. Some music files – doesn't matter what format – in my Music Library folder have just a plain white icon with a grey music note. In Music, the album itself has its artwork. I have Sync Library turned on. I've tried turning it off, restarting the Mac, and turning it back on. Didn't work. I also have Keep Music Media Folder Organized and Copy Files... both turned on. The Music Media folder location is on an external hard drive. I've tried "Organize Library" and "Get Album Artwork". Neither fixed it. I removed the songs from the library and added them again. Nothing.

Obviously this isn't the end of the world if this can't be fixed, but I am curious as to why it's happening, since it seems like it used to synchronize between Apple Music and the Finder better in the past.

Thanks.

[Re-Titled by Moderator]