Strange paint wear on rear bumper of Golf 7

[ABCD]

Hoping to get your expert opinions on the attached photo. Apologies for the quality but hopefully can make out a 10cm long strip of paint wear on the upper surface of the rear bumper of a Golf 7 90 TSI Hatch. It sits directly under the lower edge of the hatch itself, on which there is some corresponding wearing of the paint as well. The hatch is not striking the bumper when closing it and when in the closed position there is a small consistent gap between the bumper and the lower edge of the rear hatch along the whole length. The bumper itself is solidly attached without any play in it.
I first noticed a faint defect in the paint when we got the car (new) about 6000km ago but it has slowly progressed to now be through the paint in a few spots.
I can only conclude the rear hatch itself must be "bouncing" on its hinges over bumps, which might perhaps be the faint rumble I have heard on rough sections of road and which I had dismissed as being the noisy rear suspension reported by some Golf 7 owners.
Does this make sense, and do you reckon the only remedy is to reposition ie slightly raise the rear hatch hinges, or is this all becoming way too complicated for what is a small area of paint damage only visible when the rear hatch is open???

[Eaglehawk]

Oh good, so it's just not me then...