Mine has also been problemantic (!);
a) seemed to start with camera and crashing while attempting to take a photo
b) fails to shutdown in a timely manor, press and hold power button can take 5 to 10 minutes to get it to shutdown. Then takes 5 to 10 minutes to re-start.
c) today it shut down when answering a call, while connected to the car's bluetooth, (my wi-fi was off)
d) Turned wi-fi off as it drives me crazy (while navigating), pops up asking to connect to all and sundry (blocks screen), when I have the correct setting "Ask to Join Networks" turned OFF.
Today, I will re-format and start again to see if that fixs it.
I have started to recommend to all my clients to "TURN OFF" automatic updates in iOS and MacOS.