Fingerprint sensor works but doesn't.

A family member gave me their old iPhone 6s plus to repair. They dropped it screen first and it broke the digitalizer but not the glass Bought a $50 screen replacement and swapped over the home button. Screen works, home button works and no error for the fingerprint sensor. But when I go to set up touch id it begins to “scan” but will error out within a second saying “keep finger on the home button until asked to lift”. It always seems to be less than a second and I haven't gotten a single section of the scan to go through.

I've tried unplugging and reseating the home button. I've reset the phone to factory settings twice and rebooted too many times to count.

The button feels loose but doesn't have give up or down.

Does anyone know what could be causing this or why it's happening? Is it possible the home button was damaged in the drop but showed no physical damage?