Looks like they might have Recall of some sort Check out this link
So i was super happy to get the new Iphone 6s until i Found out it randomly shut off or turn off and i would have to manually turn it back on. I missed a Alarm because the phone was off at that point i knew i need to come up with a fix. Here is the only thing that has worked for me. It’s a huge pain but the only thing that worked for me.
Checkout iphone 6s gaming performance