Apple Music app overwrites separate library files with smallest library file

I have 2 separate Music App libraries — one with all my music (over 500 GB) and one for specific playlists (90GB). I switch between them by option-clicking on the Music app and selecting the music library file of the library I want to use. 

These are mp3 files I own — my personal media library with no cloud or streaming connections.

I was switching between libraries today, selecting the library file for all my music, and the smaller library loaded. I thought it was my mistake and tried again to no avail. I restarted my computer and tried again to no avail.

I thought my library files were corrupted so I created 2 new libraries and separately rebuilt them by placing the specific media folders into the “Automatically Add to Music” folder and let the music app process the media folders — this took hours.

Afterwards I was switching between the libraries to make sure everything was working properly and it happened again — the smaller library appeared when I selected the library file for all my music.

So the Apple Music App is either overwriting one of my music library files with the other or it’s not loading the library files I’m selecting.  

Both libraries are in the “Music” folder of my MacBook Pro, and I’m running MacOS Sonoma 14.6.1.