Add me to the list of people who've had issues with this. Haven't had this happen to me in the few months with the larger iPad Pro, but have had it a number of times on a 128GB Wifi 9.7 and once on a 256GB Wifi 9.7. Doesn't seem to be specific to any one app or instance, though I do regularly use YouTube, Safari, and split screen, which have all been mentioned here. I don't think it's a hardware issue, since it's just a partial restart (mine lets me use Touch ID to log back in), but who knows. I just bought my 256GB today from Apple, so it seems unlikely that Best Buy would know about this issue and pull stock before Apple even did.