Proximity sensor not working with skin

Bit of an odd one that I’ve never come across before and now I’m completely stumped.

I have in my possession an iPhone 8, everything is working properly except the proximity sensor doesn’t work with skin.

If i cover it with paper, plastic, my shirt, litterally anything, it works. The screen goes off during a call and the diagnostics app (Phone Diagnostics by Hitek Nova) verifies the proximity sensor is responding correctly.

However, if i use my hand or put it up to my face, it doesn’t respond.

I’ve removed the screen protector and case, incase that was causing an issue. It’s got the original proximity flex and display (to the best of my knowledge).