I have a different answer, and feel the need to share my frustration

BECAUSE STANDARD-MAKERS ARE STUPID

(committees, in general, always are)

One simple (simplicistic) workaround is keeping the scrollbar always around and be dealt with it

html,body {margin:0;padding:0}
html{overflow-y:scroll}

(use overflow-x for a layout that uses vh)

I believe they seriously screwed the pooch on this one.