iPhone Music app shows phantom second library after sync

iOS 18.7 Phantom Second Music Library Appearing

Something odd going on with my music library in iPhone Music – two music libraries started to appear under the (…). One a subset of the other. Then strangely the full one disappears and only a subset of a few albums are playable. 

For years I have maintained one music library on a MacBook (Sonoma 14.8.1) and use Finder to manually sync my mobile devices (iPhone, iPad) to the library. I do not use iTunes Match and do not have a subscription to Apple Music. 

The manual sync has worked fine until recently when I noticed much of my collection had disappeared from the iOS Music app, leaving just a few albums playable. It appears the ones still visible were podcasts or albums purchased long ago on iTunes. So my first step was to re-sync Music on the iPhone to the Mac. I selected sync all music and everything reappeared on the iPhone. But that’s when I discovered under the three dots (…), there were two music libraries showing: “My Library” and “Owner’s Library” (Fig. 1). Selecting My Library was the small subset and Owner’s Library was my entire collection. 

Now the real twist, after a while the library choices grey out (Fig 2) and then disappea entirely (Fig 3) leaving only the “Edit Sections” option, and only the small collection of albums in “My Library” appear. Re-synced the phone again to the Mac and the Music app went through the same cycle all over. 

This problem seems iOS iPhone specific. Entire music collection is in one library in the default location on the Mac. iPad syncs perfectly well. And as mentioned, no iTunes Match and no Apple Music sub. I am logged in to all devices with the same Apple ID and have iCloud enabled to back up the phone regularly.

Any troubleshooting tips appreciated!