Touchscreen is getting pressed continuously at multiple points

This looks like a hardware problem to me.

It occurs from time to time - after working, I close the screen cover for like 20 min, 1 hour, etc. After I open the cover and unlock Windows with the biometric scanner, I see that the screen is getting pressed at multiple points (see the screenshot). It is pressed continuously, at each of these points, and nothing can be done with the laptop. There are some limited functionalities of the keyboard still left, but neither the mouse nor the touchscreen respond to user actions.

I tried to reproduce the issue, but couldn't - it was hard to figure out the logic behind it, and to pinpoint the exact details of the use case causing this.

Recently, I had to reinstall Windows (because Dell bricked this laptop with a forced BIOS update). After that, I didn't have this screen defect for like a couple of weeks. I've been thinking it was finally gone with the reinstallation, until I saw this again tonight. 

The mouse is not available, in such situations, but I know how to power Windows off (with the command prompt), when this occurs.   

Has anybody else had this problem, and know the solution? Is there a way to fix it (without having to send the computer in for repairs)? It's on warranty, but I would prefer not to, if possible. (I don't trust these repair centers - InfoSec 101.)

I'm contacting Dell's support (but not holding my breath). 

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P.S. - This is my first and LAST Dell, for sure... (1) had to figure out and fix a problem with external mic not being recognized (the overseas support was polite, but just as equally clueless and useless); (2) then Dell bricked the laptop, by pushing a BIOS update (I ended up spending HOURS of time); (3) and now this...

Laptop is Inspiron 7786.

These points (marked in red) are getting touched continuously