I am running on OS X 10.9.5 and iOS 8.3.
Desktop Spotify is on version 1.0.7 and iOS Spotify is on version 3.3.0.
I am a Premium subscriber.
I am not even close to the 3,333 local file sync limit.
I have plenty of space on my iPhone.
When trying to sync local files on to my iOS, most of them go through okay. However, there is always a handful of songs per playlist that never sync, no matter how much I re-add them to the playlist or re-sync the playlist.
The files play fine on the Desktop version. But they are greyed out on the iOS playlists.