Start menu shrinks each time I use it

[WhiteVan]

Weird I know - but every time I use the Windows key to invoke the start menu it is about half the size of the previous time. It starts off full screen but ends up smaller than a postage stamp. Icons are the same size. It resets when I restart. I can't manually resize it by dragging the edge / corners.

Happening since the Fall Creator's Update - anyone else seen this?