random home button/Touch ID fault

I am refurbing an iphone 7.

Yesterday I had replaced everything that needed it and put it into a new housing. I test fit everything, closed the phone and everything was working perfectly.

Today I opened it up, I glued down the battery, I put on a dust/water seal, I replaced the battery/screen cover plates and closed it all up again, I turned it on and…..

“Touch ID can not be activated”

I rebooted it and then it started bootlooping…

I am a little stumped. After switching out the screen, the front camera, not plugging in the front camera at all, changing the battery (again), cleaning the flex cables and connectors, I have discovered that if I do not screw on the home button fixing bracket, then the home button works, although if I try to register a fingerprint for touch ID nothing happens, it just sits there like I am not touching the home button.

What have I broken? Is this a board problem? Have I cracked the home button flex ever so slightly? (I cannot see any flex cable damage under a scope) Did I attach a cable slightly wrong one time and fry something?

What's the most likely candidate for intermittent home button issues?

How in the !&&* can I break a working iphone 7 by just gluing down a battery and screwing the phone closed properly??

any suggestions would be very much appreciated.