iOS 8.4.1 - Lost All Music Made Available Offline

I just updated to iOS 8.4.1 and upon reboot I realized I lost all the music I had made available offline. The Apple Music app has started downloading thousands of songs, which hopefully account for all the songs that were previously available offline. Still, this has started a hours long process that I'm not confident will even work. Moreover, my phone is now overheating.

Is this supposed to happen when iOS is updated?