Cameras & torch work temporarily after restore, then stop working

I bought a 256GB iPhone 7 Plus to mess around with, and I noticed the cameras and flashlight (torch) didn’t work. I tried restarting the phone, no luck. I did a factory reset, no luck either. I did a full restore and that temporarily did the trick. After a few minutes or so, the cameras (front, rear) and flashlight (torch) ceased to function. I believe this may be to do with software, but I’m not entirely sure. The cameras don’t appear to be damaged, but I have noticed that the upper corner of the phone gets noticeably hot whenever it’s either in use, or when I used the cameras and flashlight for a brief period of time. Any ideas as to what could potentially be causing this to happen? And if so, would I be able to fix it or would I have to send my phone to a third party specialist?