iPhone SE

Hello! I have been having trouble with my 16 gb iPhone SE. I have had it since spring of 2017 and it has given me very little problems. However, starting today, my phone started doing something very weird. At completely random times, it would go to the black screen with the loading circle, exactly what you would see if the phone were dying. But after a few seconds, the black screen would go away and I would be presented with "touch ID or enter passcode". The app that I had previously been in had been closed. Other than that, the phone has been working wonderfully today, maybe even faster than normal, I can't really tell though. I tried resetting it many times, and also let the phone die completely to see if that would help. I also have low storage and tried deleting some apps and photos to see if it was reacting to the low storage level. The problem still exists. My current software on the phone is iOS 11. It has only been going on for a day so hopefully it'll just go away, but just in case it doesn't I would really appreciate if someone could help me!

Thanks,

-Claire