So basically i went to the device sync settings tab thing and went to "Summary" tab, scrolled all the way down to where it says "options" in bold and clicked the "Sync only checked songs and videos" option, synced, and now all my songs are syncing which is taking forever because i have to re-sync my 1256 songs...
In detail...
Alright i had this same problem where 30 of my songs wouldnt sync when i just added them to itunes (I had 1256 songs on itunes and 1226 on my iphone).
Then i started messing around and went to my device sync settings tab thing where you start the sync, and then went to the music tab and clicked "Selected playlist, artist ...genres" instead of "Entire Music Library".
I had nothing checked, synced, and every single song on my iphome was gone.
Then im like WTFFFFFF and clicked back to the "Entire Music Library" option and synced like 5 times and the same problem as you occurred, "My iTunes pretends like it finished syncing successfully. However, none of my media (songs, videos, ringtones, books) ends up on my iPhone."
So then i went "Summary" tab, still on the device sync settings tab thing. Scrolled all the way down to where it says "options" in bold and clicked the "Sync only checked songs and videos" option. All my songs in my itunes library were already checked, i clicked sync and applyied that change and now all my songs are syncing back to my iphone, even the 30 that wouldnt sync before and my playlists.