Apple Music in Tahoe

I switched to Tahoe a bit ago. Everything is fine EXCEPT the Apple Music app. When I opened it, the song files included only 500+ items taken randomly from my 4000+ song file in my previous Music app that are stored on an external hard drive. I downloaded the 4000+ files into the new Music app (took roughly 5 hours), and this worked for two days. When I opened Music 3 days later, the 4000+ files were gone and I was back to the 500+ files randomly drawn "songs." If I add a file to the 500+ songs, it's there for the remainder of the day. But after shutting down my computer then reopening Music, the files I added are gone.

Can anyone help me?