Nokia 8 touchscreen issues
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.