My iPhone 6 Plus repeatedly turns on and off since I updated it to IOS11.1?

I've tried resetting it different ways, I've removed everything from the phone and started a fresh but it just keeps doing it. Has this happened to anyone before?

Could be a battery issue. I had the iphone 6 before i upgraded, and it would shut off randomly. Sometimes the power bar wouldn't decrease at all, and be stuck at 100%, or drop down to around 50% and shut off.

i took it into a apple store and they replaced it with the factory warranty. I would suggest you do the same. And if they say they have to charge you, try calling their customer support on the phone before hand. As they may have more options than the store does for faulty batteries. I did that with my apple watch too.