Cannot sync music or play music to/from iPhone

In a nutshell, music won't sync to my iPhone, and cannot be played from my iPhone.

Background:

Out of the blue sky, I went in to try to play some songs from the Music app on my iPhone, and some songs were grayed out, and tapping on the greyed out ones gave me the infamous "Item cannot be played" popup. At this point, some songs could be played while others gave me the popup. I then tried to sync my phone with iTunes again, and this caused ALL songs to be greyed out and all songs gave me the popup error. After that, I attempted to delete all music off my phone by unchecking "Sync Music". This did not work, as the greyed out songs still appeared on my phone. I then proceeded to delete each and every song that appeared on my phone by hand, inside the music app, by 3D touching on a song and pressing "Delete from library". I just tried syncing my phone again with iTunes, and this time either iTunes will not sync music, or my phone will not receive and/or display music.

What I've already tried:

1. Re sync with itunes

2. Uncheck "sync music" and recheck

3. Change to select playlists to sync

4. sync 0 songs by choosing no playlists to sync

5. Manually delete all songs from iphone via music app on iPhone and then re-sync

6. Reboot iPhone and my Mac and iTunes

7. Re run iTunes 12.7.3 installer, downloaded from itunes.apple.com (did not delete originally iTunes.app first before running downloaded installer)

8. Change to "Manually manage songs" and drag and drop songs from iTunes library on Mac to iPhone. Same thing for dragging songs directly from finder.

9. Delete ~/Music/iTunes, launch iTunes again, and copy my songs back into iTunes on Mac

10. Delete music app from iPhone and re download it from App Store

11. turn off Settings<Music<Show Apple Music, reboot iPhone, turn this toggle back on, reboot

12. Re install iOS 11.2.5 via ipsw update using iTunes (update, not restore)

13. transfer songs to iPhone using AnyTrans

[NOT TRIED] 14. I have NOT tried restoring my phone to factory defaults, as I would really only like to do this as a last resort. I could try making an iTunes backup of my phone as it is now and restoring to that, which is something I also haven't tried yet.

None of these solutions worked. Now here's an interesting thing: when I launched AnyTrans for the first time, all the songs that I supposedly deleted manually from music app appeared in the AnyTrans window. I then deleted all appearing songs using AnyTrans and attempted to re-transfer my music, which also failed.

I did say "out of the blue sky," but this did start AROUND the time after I downgraded from iOS 11.3 beta 1 to public GM of iOS 11.2.5. Again, around the same time, not directly after, which is why I said "out of the blue sky"

This could be an issue with either the iPhone, or with iTunes on my Mac. Note that my iPad did not have this problem after downgrading it to 11.2.5. I also have not synced my iPad with iTunes since I downgraded it, in leu of this iPhone issue. I downgraded both my iPad and iPhone 8 days ago.

Does anyone have any idea why this is happening and any suggestions for a fix? Thanks for all your help!!

Using iPhone 6s on Verizon with iOS 11.2.5. I do not have Apple Music subscription, and I do not and have not ever used iTunes Match.

Edit: added that I don't have Apple Music subscription