I now have this problem, too; iPhone 8 plus a little more than a week old, but I have had no problems until today. One thing that is fishy is the AppleCare online diagnostic...within an hour or two of doing the diagnostic (and having to agree to send data to Apple and their ad buddies, or whatever the disclaimer said), boom—constant crashing, spinning icon in the center of the screen, kicked to locked screen.
I have had no problems with my old 6s for two years. ****** about my new phone not working, I grab the old one that has been off for a week and attempt to use that. Boom. Doing the same thing!
Both have 11.1 on there...trying to update to the 11.2 release, but, well, THE STUPID PHONES KEEP CRASHING.
The Apple community misses Steve Jobs more and more with every single Apple release nowadays.