iPhone 8 proximity sensor failure after screen replacement

[paardenkapper]

Hi all. I work for a company that hands out iPhones to employees. Lately we got one back with a hole in the screen and I decided it was worth repairing so I bought a replacement screen on eBay.

This screen would come without the Home button - understandibly - and minus the whole speaker assembly, front camera and proximity sensor. Yet after carefully transferring all components from the broken screen to the new one the iPhone would not boot. It stuck in the apple logo bootloop forever. This ended after I unplugged the upper cable to the camera, proximity a.s.o. and the phone worked as it should.

Upon inspecting the the flex cables I could not find any obvious damage. Can someone tell me if it's possible to repair or what to look out for?
Thanks.

 

[Imac Sam]

I used to repair Iphones a few years ago and at a temporary job choice. When you removed the sensor package originally, one of the adhesives act like an insulator against the metal of the of the phone. When you are changing screens it gets left behind when trying to remove the sensor. If I remember correctly it was a small black square of adhesive that needs to be replaced/reinstalled to keep it from happening. There are some metal contact pads under it. If you no longer have the small black adhesive pad, it is those contacts that ground against something and are causing your constant reboot. So get the thinest piece of tape you can to at least cover those contacts. The circle in the pic I attached is the black adhesive pad of concern. Hope this helps.

 

[paardenkapper]

Well now that is valuable information!
I'll try that out as soon as I find the time and reply with the results.

 

[paardenkapper]

@Imac Sam

I just took photos of the screen assemblies.

Left is the new one - on the right is the old one.
Where would that adhesive go?

Here is my camera module with sensors - thanks a bunch!