Following replacement screen, touch doesn't work?

I changed the smashed screen on a 6S plus. Before exchanging the screen I tested the damaged one and it was fine in terns of touch response.

After I changed the screen over for the new one, the phone powers on, and displays fine, the home button works fine, but the touch response does not work at all. Suspecting a potential faulty screen, I exchanged back to the damages screen and it is also the same (powers up etc ,displays but touch response not working at all). I've tried hard reset etc and nothing resolves it. I've inspected the logic board plugs and the pins look aligned and fine. Any ideas?