None of my music synced from iTunes (12.1.2.27) is showing up in the Music app and iTunes shows all the space on my device as "other" and won't sync. I can see the music on the device via iTunes (and can even play it) but can't find it or play it on device.
same here after update iPod touch (Gen 5) to ios Beta 9.
Lost all the music on the iPod. The checkboxes are still marked in iTunes but doesn't sync the music. The Rest (App, Contacts, Calendar, etc.) is still there.
On the Mac is 10.11 beta installed.
I have been fighting with this problem for weeks now.
A big problem for me is that my itunes library is large and for some reason my iPhone crashes when it has tried to sync with iTunes, therefore interrupting the sync.
The Apple move to streaming is a disaster. Even music that I have bought and bought a high capacity iPhone to store locally does not go on to the iPhone any longer and as a result I need to either download it via wifi or not have any music on my phone.
My only fix was a complete restore and back up from iCloud that doesn't have music or photos. Then you have to try and find a way to get the music onto the phone without syncing via a wire.