IOS 8 iTunes sync problem

Question

I bought a 128GB iPhone 6 Plus in order to sync all my music. When I tell iTunes to sync all my music, it does so (takes over an hour) and my phone shows as having 80GB of Audio. All the music plays on my phone.
However, without making any changes, the next time I plug in the phone *all* of my music becomes unplayable on the phone. Each track just skips immediately to the next and each is marked with the 'square in a circle' icon.
Now when I look at the used space on my phone in iTunes, the 80GB of Audio has changed to 80GB of 'Other'. The music won't play on the phone and there's no way of removing that 80GB of Other without wiping the phone.
What's happening?

Answer 1

Yep, exact same thing happened to me.  I have synched my Iphone 6 128gb many times without issue, and adding new playlists/tracks.  Then suddenly yesterday it got hung up on the synch step "waiting for changes to be applied" and all but about 15% of my music was gone from my phone.  The playlists were showing up but they were empty.  Reset the phone, restart macbook, no change.  After multiple attempts, I was finally able (don't remember how) to re-synch my music to my phone, however, now I have 40gb of music & 40gb of "other" using storage.  It's as if there is a ghost copy of my entire synched library stored in Other, with no way to delete it because it doesn't show up under "Usage" in Settings.  Which really *****, b/c now I only have 19gb of free space on my phone when i should have about 50gb.
I am reading that many people are having multiple issues with synching music so this is a common problem.  It is very annoying, i'm glad I was able to get my music back on the phone, but i'm afraid to plug it in again as it might delete the music again, or put even more into Other.  And I can no longer edit what music and playlists I have on my phone.  This is a basic function of itunes that is now failing.  What has happened to Apple quality control?