Having exactly the same issues on my iPhone 6S. Camera randomly takes forever to load, and sometimes doesn't load at all (black screen). Since iOS 11 it's a 50/50 chance that accepting an incoming call works. I press the green button but it keeps ringing until the other person hangs up. Even physical home button becomes unresponsive, many times a day I have to do a forced restart (home button + sleep wake button pressed). This is infuriating!!