Device Storage Full?

I have 100mb available left on my phone and the app wont let me play any music now because "the device storage is full" which makes no sense because A) I still have room on my phone, and B) I can still listen to music on iTunes or Spotify even if my phone storage is full. Why does this happen and can you please fix it?

I ❤ games 101 about Google Play Music, v3.38.1007