I am having this issue as well. I cannot sync music, nor delete any music off of my device. I have tried deleting from the music add. under usage settings, and in iTunes itself. Also, the music that is on my device is now taking up double the space. I have a 14 gb library that is showing 28 gb on my device. The songs are only one the device once and are not playable. The 28 gb of music is now taking up the rest of my memory on my phone and I cannot take photos or sync any other content.
On a related note: music syncs but then the shuffle plays a single song and stops each time.
Had to add the app, djay to get the shuffle working again.
I was having the same issue. I unregistered my device from my icloud. and reset the phone. Then I set it up as a NEW IPHONE with NO ICLOUD and set up itunes and synced the music first. Then I went back and set up icloud and got all my contacts and everything else back. All my music works now and everything else is perfect too.