Many (not all) offline songs not syncing to iPhone 4

[GratefulEd77]

-Over 3GB available on my phone (current updates of ios and spotify) 

-Some songs sync, some don't. In some cases the album artwork will even appear, but song will not play 

-Phone and laptop (home library) on same wireless network 

-What's really baffling me is that some of these tracks do sync. The answers I've found here would probably be helpful if NONE were syncing, but I have plenty of songs that do sync.

-Premium user, only about 350 - 400 songs from my personal library marked to sync offline 

-About 1150 total tracks marked to sync offline 

[Peter__]

Can you see your iPhone under Devices in the desktop client?