Sorry to hear you have issues with IOS 11. I updated my iPhone 6 Plus, wife’s 6s when it first came out along with two iPads. Have had no significant issues. I’ve had some minor things dealing with photos but don’t know if it’s related to IOS 11 or just the app as I didn’t use photo library in the cloud before now.
Have since upgraded to 8 Plus and regular 8 phones and things are going good with the exception of the photo thing. I’m always amazed that with millions upon millions of devices out there, with different chipsets, software mods by the telco companies, that actually so few folks have issues. Hope you get your problems resolved quickly.