my phone also is having a score of difficulties, all revolving around wired sync for the music library. In order:
- Began taking far longer to complete sync, seeming to hang at the part where it gets ready to sync tracks (checked music, checked playlists, new additions to the desktop library)
- Proceeded to declare almost all of my onboard music files ineligible for playback because of region issues, for files that were *local data to the mac*
- above prompted removing all music from the phone and reuploading them, restoring my legacy music collection
- new problem: the latest dozen or so tracks appeared as present in library, but playing them would result in other songs in collection playing. Now they won't resync to phone.
mobile device: iPhone 12 Pro with iOS 18
desktop: 27" iMac 2018 with Catalina 13.7 (latest catalina update as best I can tell; hadn't upgraded yet because a friend and others online had been running into USB connnection errors)
EDIT: After deleting the tracks, removing them from the desktop library, re-adding them to the library, and trying multiple sync attempts, including having to unplug and plug the phone back into the desktop, the songs finally are back on the phone and working again.