Phone not booting when home button cable bracket is in place

Folks,

There is something very strange with my phone. After installing a fresh screen the phone does not boot when the little bracket of the homebutton cable is in place. I'm talking about the little 6 by 2 mm bracket with the two holes.

However, when you turn it on before you close the phone, put the bracket in place, close it, it stays switched on a works like a charm. When you then turn it off, it does not power on whatsoever (screen stays pitch black, no vibration).

When the phone is open, it can be readily switched on again.

Tried: another fresh screen, new battery, isolating almost everything to prevent short circuiting.

I subsequently left the little bracket out, and everything worked as before (including touch ID etc).

What is happening?