Why is my phone detecting two taps instead of one on the screen? I'm observing a strange behaviour on my phone out of the blue. Yesterday, the left side of my screen stopped working properly. I started having a hard time clicking anything next to the left edge, typing the keyboard or pressing buttons on the left. 

I enabled Developer Options > Input > Show touches, and I was able to observe that when I try to tap the left side of the screen, the screen appears to detect two taps on opposing sides of a column, as if the whole column of pixels were damaged. The phone hasn't suffered any hits or gotten wet. This is just out of nowhere. 



I've uploaded a video of this to make it clearer here.

This is an Xperia Z3, D6603, running Android 5.1.1.

Has anyone encountered something like this? I've tried restarting the phone to no avail.
This is a hardware problem. The screen sensor is faulty. The actions most likely to solve the problem:


Factory reset
Cleaning of the screen ribbon cable 
Replacement of the screen.