Hi, I had exactly the same issue as yours. It's not a software problem, it's a camera connector issue (at least in my case).
You need to turn off your phone, remove back cover (screw out two small boots at the bottom of your phone first). After that you need to remove plastic protective shield from the motherboard. Attention, your varanty is now void!! And the last step - disconnect camera connector and connect it back. Put back plastic cover, back cover, and turn on your phone.