Nokia 8 touchscreen issues It's a brand new Nokia 8, running Android Oreo 8.

When the phone is lying down on the table, the touchscreen becomes somewhat unresponsive. The effect is increased when it's plugged in for charging.

If I touch the screen, the touch does not register on the correct point, or if I draw a line, it breaks off into multiple dots or dashes. On picking the phone up, the issue sort of disappears.

I don't remember the brand name of the tempered glass screen guard I have, but I think it's of good quality, and do not believe it's an issue. 

Some users on Nokia support have said they don't have any screen guards installed, and yet they have the touchscreen issue. I see that many users on XDA have the same issue as well.

I contacted Nokia support via the built-in app, and their response is that I should bring it to a service center for a close examination. I will do so later.

I'm keeping this question here for posterity. Maybe somebody will know what's going on.
Blame electrostatic charge for the fault.

The touchscreen in modern phones and tablets is capacitive. When you put your finger on it, your finger and part of the screen forms a capcitor, which allows the touchscreen to determine its position and size by examining its physical indications.

When there is unwanted electrostatic charge, either from another charge source like a metal furniture, or from a badly grounded charger, it can mess up the detection of capacitor of the screen, making it into thinking you're tapping every where. This is the cause for the strange behavior you see.

The solution is to keep your phone away from electrostatic charge, or release it if you happen to see the misbehavior. Releasing charge can be as simple as touching something metal and well-grounded, or touch your phone while you are well-grounded.