Rob Griffiths is the kind of Mac geek who gets tech support from Tim Cook, and even he is struggling to keep iTunes sync working. The list of presumed bugs and magical workarounds for sync failures and Metastatic Other (CloudAssets cache bug), continues to grow, though no fix has been quite as exotic as my restoring from iCloud when restore from iTunes failed or @gaelicwizard’s suggestion to sync from a foreign computer to fully reset sync.
I see all of the problems Rob sees — and more. I really do miss the reliable days of iPod synchronization to iTunes. 
There’s rumor of some sync fixes coming, but what I’d mostly like to see is error logging in Console. At least then we’d have a fighting chance at debugging this kludged mix of Cloud, USB, OS X and iOS.
Today’s problem was failure to sync my daughter’s music to her often troublesome 4s. I tried all the usual incantations including a “restore” (wipe) and restore from backup , and as usual nothing worked. iTunes sync swallowed its errors as it always did, and I saw long lists of dashed circle icons next to her phone music list (means sync failed).
Given Rob’s article I looked for dupes and I found an odd set in the music library:
Internet audio stream dupes?! That’s another bug, they aren’t supposed to show in Music — they’re “radio stations”. I deleted them, but it didn’t help.
What worked was kind of odd — I think the Wipe/Restore helped a bit with this, but it wasn’t enough by itself. I walked through iTunes long music screen, removing all the albums, playlists, manually added tunes and so on. Lots of clicks, but I didn’t uncheck music sync. Eventually I got all the music off the iPhone. Then I created Playlists and consolidated them with another “union” playlist that merged every playlist. Then I set that, and only that, playlist to sync. It worked … almost. Of 433 songs in the consolidated playlist, 432 actually show up on the iPhone. Turns out one of them is “Explicit” so was blocked, it shows as “dotted”.
I think this phone has some Flash problems, but maybe the single playlist sync source helped workaround what sounds like some nasty bugs with reconciling duplicates. Or, more likely, it’s all voodoo .
 Synchronization is Hell. Gotta admit though — Calendars5.app/Google Calendar and Contacts.app/iCloud still mostly work, Toodledo/Todo is very reliable, and Simplenote/AltNV hangs on by its wee finger nails.  I wonder if the voodoo depends on whether the phone stalls out on a bad bit of memory. We need those missing Console diagnostics.