My iPhone 8 plus screen gets black shadow - post I hang-up an incoming call

Hi Everyone,

Am facing an issues with my iPhone and since last month I have made numerous calls to Apple support and they tried resetting etc but nothing worked until now.

The problem I am facing is as under:

Whenever I get a incoming call and I speak to the caller and hang-up, I observe that my home screen is pitch black. When I press a home button or swipe screen I get back my original screen with proper colours i.e. without any black curtain on it. I succeeded in capturing the screenshot and control center same is attached for reference.

Please suggest how to get rid of this. Until now it was happening once in a while and not for all the incoming calls. But today 2nd November it happened so far on all the three calls I received in morning.

My iPhone has standard wallpaper i.e. Apple default which came when i bought phone on 29th September 2017.

Please help.