iOS 8.4 update erased my music

I just updated to iOS 8.4 (iPhone 6 - 64 GB - Verizon) and was dismayed to find all my music (save songs purchased directly from iTunes) had been erased. I plugged my phone into my computer to re-load all my music only to find that all 16GB of it now shows up as "other data" which the phone does not recognize as music and I am unable to get rid of. I put all my songs back on by syncing my library, but that massive block of unusable data remains. How do I get rid of it?