Oh, one more thing, I had my music library get pretty borked (album art and such) when upgrading to iOS 8. Simply unchecking the music and resyncing didn't do it for me. What I ended up doing was a "factory reset" (it re-downloads iOS 8) and then a restore.
After that, my music and album art sync'd... OKish. A few iTunes purchased albums - just 4 to be exact, but it was enough - they messed up the Albums list. They appeared in the right place, but they'd put the "R" designation above an album by an "A" artist. That made the navigation by letter nonfunctional. Broken. Kaput. It ceased to be. The only way I could fix it, finally, was to remove those albums, convert them to MP3's in iTunes (I know) and resync.
iTunes Match was a complete debacle for me when it launched, and then iOS 7's music player - I used to think of them as the best company for music, since their iPods are the entire reason I ended up with iPhones (and then Macs), but sadly this opinion is fading.