Hi
Well I've battled for days with this one, and tried many of the above suggestions.
I told iTunes to sync selected playlists, abulms, artists, genres and then selected a few artists at a time
In doing this (and watching my iphone)I discovered that the process seems to be
- each album is added initially, using first track only (other tracks greyed out)
- as process continues, tracks are added
- for no apparent reason sync process stops, at a (repeatable) offending track
- all tracks not yet synced are left greyed out on the phone.
I tried unselecting the offedning artist, applying (re-syncing) which worked intermittently, but not for all offending instances..
What has 100% worked for me now is to run mp3 Scan & repair to identify offending albums/tracks with ??corrupted mp3 tags.
Each one it identified I deleted from library/iTunes and then re-ripped from CD or FLAC, and then added back into iTunes.
This has resolved all problems:-
A week ago I had partner & my iPhone 5's with no music.
After one week of trying, my partners phone eventually had a full library, after painstaking trial and error until I stumbled on the above. (yes, it has been a mammoth 100+ hours of waking time)
Now my own iphone is happily syncing all 6000 tracks from the same library with no hiccups, should be finished in around 4 hrs, a total of about 10 hours.
Phew
HTH