Hole in plaster behind up high kitchen cupboard

Thanks ladies. It is below the bathroom. All as dry as a bone.
The cupboard hangs on two metal fittings. The top of the cupboard is about 12” from the ceiling.
We’re thinking that the fitter has maybe caused damage to the wall and just hung the cupboard over it.
Why I only noticed dust recently is a mystery. It’s a worktop that gets a lot of use and have I been wiping the dust up for a long time when cleaning/clearing the surface.

Dh has the hole filled and the cupboard rehung.

Hopefully that’s the end of it.
But I do like to know why ......

There could have been a gap in the base which the plaster covers ? This would cause a hole to appear if there was no backing, like a space in the slat .

I hope i am wrong but you may want to look into dry rot.
A neighbour had the same type of thing years ago.

I've been thinking back. It must have been 10 or 12 years ago that the storm damaged the roofing felt. I only noticed the ruined patch of plaster a couple of years later because it wasn't covered up. Yours is behind a cupboard, so it could have been damaged 12 years ago somehow and been invisible ever since, That doesn't explain why it has started crumbling away now, but it might explain what caused it to be fragile in the first place.

Look wider than the kitchen. For instance, does it back onto a bathroom? We moved a tall bookcase in our dining room and discovered the plaster behind it was falling off in sheets! On the other side of the wall was the shower over the bath - the seal between the bath and the tiles was disintegrating, so water was gradually leaking through.

What is above the kitchen? If there is a bathroom up there, perhaps water is slowly leaking down the bricks and exiting behind the cupboard. If it wasn't much at a time, it wouldn't take long to dry, but it would still weaken the plaster.

It could even be an old leak which isn't there now, but the plaster has weakened as it dried. We had to replace the roofing felt over a dormer window after a storm. We thought the room had escaped unscathed, but two or three years later, I noticed a small rough patch about four inches across on the plaster of the coombe ceiling near the window. I prodded it with my finger - which went right through! It was exactly where there would have been drips. The plaster and the lathes behind it were bone dry, but the plaster was powdery and dusty and came off with the least pressure. Yours sounds similar.

There could have been an air bubble in the original plaster?

Thankyou geekesse.
We have so many questions..... What caused the hole??. Wall skimmed 12 years ago to install the kitchen.
The hole is nowhere near any air vents or plumbing.
Nearest window is two cupboards distant. Nearest air vents is three cupboards distant on the other side. Nearest plumbing is at ground level where mains water feeds to the sink. There is no space around the hole giving access to any draft from an airbrick or such.

The hole may have been there for some time. Recent wind my have caused a draught inward through an airbrick or a gap in the wall where pipework goes through, and blown the dust from the edge of the hole in the plaster on to your kitchen worktop.