Same thing happened to my iPhone 7 Plus. I called and told Apple customer care about the problem, they said that even though my phone was out of warranty since it’s a known issue with the update they would replace it. I took it to the Apple Store and they said it’s a good thing I called and spoke to an executive because they would have charged me $349 but since he had put a case # on my issue with instructions to replace the phone at no cost they didn’t charge me. So call and then go replace your phone.