Music library is duplicating, deleting, unable to sync, etc.

I use the music app, subscribe to Apple Music, and use iCloud Music Library to sync music not available on Apple Music streaming across my devices. It's worked beautifully for a couple of years.

In the last few weeks, everything has gotten screwy. I will import a CD (or sometimes just music files, typically ALAC but sometimes other supported formats) and the Music app will update the Cloud Library. It will all seem fine (and appear on my iPhone, etc.), but when I return to the Music app, many of those same music files are now missing. Almost invariably, when I click on an album, each track now appears duplicated – one is on the hard drive, followed by a duplicate with the "download from the cloud" icon next to it. (So if I played this album on my Mac, it would play each track twice.) If I delete the duplicates with the cloud icon and just keep the ones on the drive (a torturous process), it seems fine but hours or a day later, every single track now has the cloud-with-an-x-through-it icon, and if I click on that it tells me it won't sync, or doesn't exist. And now they're not on my iPhone (etc.) anymore.

My imports from weeks ago to years ago are all still working fine. It's only new imports that are having this problem. I deleted my .itl and .xml files, which briefly looked like it had cleared up the problem, but no such luck. Sometimes, I drag the files into a folder, delete them in Music, then reimport them. For a while, this seemed to work, but in the last few days, it doesn't, even if I try multiple times.

For the most part, these are .m4a files generated by Music (importing an obscure CD), so they certainly should be completely compatible.

Anybody have any suggestions? This is driving me crazy!