Spotify got an update a couple days ago. My phone also became very sluggish and unresponsive a couple days ago, but I had no clue why and wasn't aware of the new update. I even tried factory reset before I relised Spotify had had an update and it might be the one wrecking havoc. I deleted the app and everything went back to normal, my phone is working again.
EDIT: It turns out it wasn't spotify that was making my phone malfunction. The freezing and rebooting came back pretty soon. Either the OS is going crazy or it's a hardware problem. My phone is being maintenanced now.