After almost 2 months, i already know the reason why my songs/playlist in latest itunes do not sync with ipad 4 after upgrading to IOS 7 even if these songs/playlist were in my ipad when it was still IOS 6.
IOS 7 do not recognize nor sync songs which have special characters in the details of the songs ( artist name, title, type, etc.). That is the reason why when i tried syncing songs/playlist, some playlist worked and some don't.
To solve this problem, here's how:
1. Open your itunes and choose your music library.
2. Choose a playlist on the left side of the menu and/or choose the songs viewed on the right side of the screen.
3. Check the detail of the songs by choosing a song, then right click>choose "Get info"
4. A menu will appear which contains several tabs (summary, info, video, sorting, options, lyrics, artwork)
5. Choose "info" tab.
6. Now check on the details of the song (name, artist, album artist, album, grouping, composer, comments, etc.)
If it contains any special charater like o, @, or any other ascii characters, delete that character and click ok.
Once finished, try to sync the songs or playlist again.
Auto syncing should now work.
Hope this helps.