This is a problem for both iOS7 [iPhone 5c] and the Apple OS X [Macbook].

My girlfriend, a Spotify Premium user, recently upgraded from an iPhone 4 to the 5c in late October..  After she transferred all of the data and synced her new device, Spotifly will no longer play many songs that it used to.  Spotify is currently up-to-date on both of her devices. 

Some of the songs she has stored locally on her device, downloaded from the Spotify service.  Some simply won't play off streaming directly from Spotify.  Sometimes, the song's track time elapsed counter and sliding progress bar will increase as if the song is playing, but no sound plays, not even static.  Other times, the counter does not appear, and the progress bar is grayed out, as if it were searching for the song. 

Any assistance is appreciated.