Earlier quoted context omitted.
This can happen in native UIs as well. I've had to add hysteretic behaviours to prevent the appearance of a scroll bar somehow obviating the need for the scroll bar, so it vanishes and now it needs a scroll bar, repeat as fast as the toolkit event loop allows.
This is why everyone switched to overlay scroll bars. It's also better for performance because you don't need to do layout on a screen worth of content only to realize you need to reserve 16px and do layout again.
And an additional complaint about those tiny-thin scroll bars that some idiot-designer though were slick because they so minimally interfere with the rest of 1920px-width display, which also makes them a giant pain-in-the-wrist to click on because the width to make it appear is so thin, and then clicking on the scroller is another challenge whereby it's much easier to accidentally make the scroll bar disappear. Rinse and repeat.
I used to be half-decent at railgun in Q3A, but I now struggle to hit scroll bars. That's a fucking design problem.