New screen replacement not working

I have done 30+ iPhone 6 screen replacements. This one has stumped me...

A customer brings in an iPhone 6 with cracked glass. Everything functions fine. I've replaced the screen with several different complete assemblies. The iPhone will vibrate, pause for a few seconds, and then loop.

Put the original screen back on, everything functions fine. I rather doubt that five LCDs could be bad. Is Apple booby trapping their LCDs like they do with the fingerprint scanner?

I've tried holding down the power and home button.

I've tried unplugging the battery.

Any insight would be helpful.

Thanks guys!

Josh Muir | EXPERIMAC