I have also been experiencing similar connectivity issues with my 6S Plus since upgrading to ios 11.1.1 and/or Verizon's 30.1 Carrier Settings. I am not sure if one of the updates or both of them is the cause of the problems since I updated both around the same time unfortunately, but I am certain it is one or the other (if not both) as there has been no physical damage to my phone and I have a different iPhone on AT&T that is experiencing no such issues (also updated to same ios).

My problems seem to relate mainly to WiFi and text messages. First and foremost, available networks won't even appear when I go into Settings -> WiFi. Only if I turn the WiFi radio button off, then back on again will some networks then appear. However, the number of networks that appear is significantly smaller than the number of networks that appeared before updating to ios 11.1.1 and Verizon's 30.1 Carrier Settings, even from the same location. Additionally, sometimes I receive strange messages like "Cannot connect to X network" and "Incorrect WiFi password" even though that password is stored and that same stored password works on the same network at other times. When I finally can connect to a WiFi network (which is rare), if the screen shuts off or the phone goes to sleep due to inactivity, the connection will be broken when the screen/phone wakes and I will have to manually go back into Settings -> WiFi, turn the WiFi radio button off, then back on again, and try to connect to a network (assuming it actually appears in the list of available networks, which is hit-or-miss). This is ludicrous.

I've tried all the suggested solutions I could find online, which are primarily to hard reset your phone, reset your network settings, turning off certain new features and turning them back on, and doing a factory reset on your phone - none of which solved my problem. I also have an iPhone 6 that has been experiencing no such problems since updating to ios 11.1.1, though this device is on AT&T's network and not Verizon. This makes me think this problem is isolated to either the iPhone 6S+ or devices using Verizon's network/carrier settings, but it seems like the original poster has iPhone 6S so likely not isolated to just the iPhone 6S+.

Has anyone been able to find any sort of solution to the connectivity problems people on Verizon with iPhone 6+ and iPhone 6S+ seem to have been experiencing since the update to ios and/or carrier settings? OTHER THAN hard resetting the device, resetting network settings, and doing a factory reset on the device?