This is one of the most annoying bugs in the iPhone: it randomly removes large chunks of music. For instance I was in a mood to hear Christmas songs on a flight the other day so I loaded one of my Christmas albums. As soon as I clicked the album to start, I can see the UI flying through the songs one by one since none of the songs was present. I have to be back on the ground and re-download these songs, which is incredibly annoying. I looked in my iPhone Music settings and I don't see anything that would indicate the iPhone is trying to save space or anything. My new 128GB iPhone 6 is on its way to me now, so maybe once I have that I won't have this problem anymore, but it's SOOOOOO frustrating and I can't figure out how to fix it. Does anyone know how to get around this? The whole iPhone music and syncing with iTunes is just a nightmare and it's shocking that after all of this time, Apple still hasn't "figured this out." It doesn't "just work" like most Apple products used to claim.