If you recently rebooted your phone, you might have noticed that for no reason whatsoever all your locally cached music on Google Play disappeared. It’s a bug and it’s being addressed, although the rumor mill seems to be running rampant that it has to do with DRM or copyright infringement.
Nope, it’s a bug and Google is aware and working on it. It also supposedly only affects music stored on the SD card, however whether they’re using that term to mean a distinct microSD device or anything mounted as /sdcard, I don’t know.
In the meantime, the only solution for offline music in Play Music seems to be to sideload any music you want to your devices, or simply not reboot your phone… ever. This doesn’t work for items you’ve purchased through the Play Store however, as you’re not getting them in a sideload-able format without breaking a few copyright laws most likely dealing with reverse engineering a DRM scheme.
As some of us use old Android devices to cache days worth of music for house audio, it’s a pain when the music device reboots or a baby decides it’s time to unplug the unit and let it die. The resulting gigs worth of re-caching can be a pain.
On a side note, if you’ve got a phone laying around doing nothing because you upgraded to the fancy beast, let me suggest turning it into a music station triggered by Tasker and Autoremote. I never really appreciated how funny it would be to show up at my house and walk in to my own theme song.