Why won't all songs download in 'Available Offline' playlists on iPhone?

[Media_Scotland]

I've got a Spotify Premium Account, I've got plenty of storage space available on my iphone, yet there's hundreds of songs in my 'Available offline' playlists that won't download. I've been trying to download them for weeks now by starting then restarting my Spotify app.

Can anyone tell me why these songs won't download onto my iphone?

I have iPhone 4S, updated with latest software, same with the Spotify app. 

One thing that may help you guys is that when I launch Spotify on my iPhone it does start downloading songs (Downloading 2 of 356 for example) but after a few seconds the download bar dissappears.

Any ideas how I can fix this so that I can listen to all of my because just now, not all of my playlists are "Available offline'!!