This is my Bizarro Problem.
For a while, I have noticed that my iPhone has lost some of the music files when I sync to the Mac. First it was CDs that I had ripped, and therefore was not associated with an apple id, then it was some music I had downloaded through iTunes.
This week, with iOS8, I decided to upgrade my 5, and I got a 6. I am not using iTunes Match.
Back up to iCloud
Encrypted back up to iTunes on the Mac
2-b - download and installed iTunes 11.4 - rebooted.
Downloaded and installed iOS8 on my 5 successfully
Picked up 6 today, set up by restoring from my encrypted back up on iTunes
All Aps, photos, settings, passwords came over fantastically, Music did not. only 300 of 3800 songs synced.
Went to Music, made sure Sync Music was clicked, and Sync Selected Songs, the blue Audio bar expanded, and I started the sync. It quickly went through the 4 steps to begin copying songs - and then abruptly stopped. this took less than a minute.
Tried the above with sync all music. I have 50 gig of memory free, so I have room for the library.
Switched cord I was using between phone and computer
Rebuilt iTunes library - which got me to 1400 songs, rather than 300, but still not what I want.
And that is where we are at.