Can't play my mp3's on my iPhone Music app

I'm a musician and radio DJ with a large mp3 music library (not purchased from Apple) loaded in my MacBook Pro that up to about January 2025, I used to successfully sync music files and playlists to my iPhone 13. Something changed and while I can see song titles in playlists (downloaded from MacBook), they are greyed out with an error message 'This item is not currently available in your country or region'.

I've deleted all music files from my iPhone and tried to reinstall. Some files will transfer and play, but 99% of the playlist songs will not. Greyed out song titles in the iPhone PLAYLIST are not listed in SONGS (See attached image). I've been researching this problem for quite some time and trying many workarounds. I'm trying to determine if this is a Professional Recording Organization (PRO) licensing issue that Apple software is having with ASCAP, BMI, SESAC or an Apple FairPlay is a DRM (Digital Rights Management) issue or something else. I've seen many posts with iPhone users struggling with the same issue and see no viable solutions. Yes, I've checked my Country setting (United States) and several other end-user suggestions with no luck.

I'm planning on upgrading my iPhone 13 and would like to go with the iPhone 16 Pro, but if I'll have the same problem, I'll look towards an android or other.

Can anyone from Apple tell me what the problem is? Thanks!

[Edited by Moderator]