IPHONE LOCK SCREEN

[JammieR]

Its been a year now for me to use iPhone 7 plus. Initially, it was fine but then it started malfunctioning!!
What it does now regardless on which app I am on it locks the screen and I am being thrown to the start of the phone where I have to unlock it first with finger impression and then use the phone.
Is there anyone who had the same issue or is having this issue. Please help me out with this thing.

 

[JammieR]

Is the sleep/wake button sunken in? So when you;re using it it thinks you've pressed it therefore locking the device and requiring you to unlock it again?

Offcourse not. That would be quite evident if this was the case and I would change the button. But things are out of control because I am unable to find the issue.