Wi-Fi greyed out, no flashlight, camera issues after screen repair

Hi

Today a customer gave me an iPhone 6 which he alledgedly 'fixed himself': he changed the LCD Digitizer assembly because it had a huge crack in it.

After installing the new assembly and booting it up, following things started going wrong:

• Wi-Fi and Bluetooth stopped working; Wi-Fi toggle button became grayed-out
• Rear facing camera worked, but couldn't take pictures. Hitting the big white button in the camera app did not take the picture anymore. Front facing camera worked completely fine.
• Flashlight does not work anymore
• Leaving the phone on stand-by for a couple of minutes will lock you out completely: it won't power on anymore, and you have to reboot by pressing POWER + HOME simultanously

What I tried:

• Putting a cracked, but working OEM assembly in place
• Disconnecting the camera
• Cleaning the connectors
• Disconnecting just about anything but the battery and the LCD / Digitizer
• Software reset to factory defaults

None of these things changed anything. I already told him it's probably a lost cause, but I'm curious what might have caused this. I've seen several topics online with people having the exact same issues. Any ideas?