Display does not respond to touch

Phone was dropped, then the touchscreen became intermittently non-responsive. Applying pressure to the sides of the device or providing some flex would get touch functionality to restore for a while. Eventually even this stopped working and the touch functionality stopped working entirely although the display itself is still perfect.

I figured this must be a screen issue though I dont understand why only touch would fail and not display; so I ordered a replacement screen and hooked it up to test but again have the same issue, display works perfect with no touch input being accepted. I inspected the connector/board for the display and don't see anything wrong (although I dont have magnification). I cleaned the board side of the connector with 90% IPA though it made no difference.

Anyone have an idea of what to look for? I understand I will most likely need a new phone at this point but I'm still interested in what went wrong.