Folks, this may be a problem with the CPU types used within families of handsets being slightly incompatible and nothing more. Everybody, please download the app "iPhone battery memory system status monitor". It is a free app that identifies the health, memory available, CPU performance and specific chipset used in your phone. Very handy. Touch the "System" tab at the top. Under the first header "Device" you will see "MODEL", to the right is your CPU part number. The iPhone 6S will have either N71MAP or the N71AP. Only the iphone6s handsets with N71AP appear to have iOS11 lockup problems. My malfunctioning iPhone7 with iOS11 has the D101AP processor. The other processor type in iPhone7 is the D10AP.
Please help to identify if iOS11 is specifically INCOMPATIBLE (at the time of this post) with N71AP (iphone 6) and the D101AP (iphone 7). Even if your phone is working, please indicate your CPU here to see if there is a trend to the actual CPU type being the true culprit! For iPhone7+ users, you will either have the D11AP or D111AP processor. There may be subtle differences between the processors causing this nightmare. All other phones with or without ios11 incompatibility, please report your CPU here as well and whether or not your iOS11 is working to see if there is a pattern.