tripple-clicking your home button will invert the colours, and holding it will activate siri.
This could be a short in your flex, on the connector, or a mechanical pinch of the button.
-i would suggest removing the new screen, but keeping it plugged in. test the button with the screen apart from the frame. if this fixes the issue, it is a mechanical pinch, and you need to sort out how it fits in your frame.
-be sure you have taped the digitizer circuit across the bottom with electrical or Kapton Tape.
-make sure the home button slides nicely between the LCD And the Frame.
your home flex ribbon may be shorted, in which cas you will need to re-replace it
You could have the connector to the Motherboard having a loose pin. in which case you will either need to realign, or replace that connector.