Chosen Solution
I bought an iPhone 7 with a screen that had a single crack in it. Tested it and everything worked fine including touch id. Had an extra screen laying around that may have been water damaged and thought I would test it just to see if it worked, which it didn’t. When I connected the old cracked one back touch id wouldn’t work anymore. First it reacted like I was double tapping. Inspected every cable and pin, but can’t find any breaks. I also did an DFU reinstall, but touch id still won’t work. When I try to add a fingerprint it doesn’t register anything. The home button works fine besides touch id. What could the fault be?, could the screen I test fitted have caused damage?. When I removed the old screen I didn’t touch home button flex cable, but could damage to the other three flex cables that connects to the logic board result in symptoms like the ones I have?
Got the new screen and the culprit was the flex cable on the screen itself. Changed the screen and now Touch id is working .
if the homebutton is super sensitive then its usually the flex on the actual homebutton that is damaged.(usually from opening the phone wrong). Also check the flex on the screen, its the smaller connector that is responsible for the home button and is easily ripped where it bends through 180deg.
