Chrome Version       : Version 70.0.3538.77 (Official Build) (64-bit)
Other browsers tested:
     Safari: OK

What steps will reproduce the problem?
(1) Go to https://en.wikipedia.org/wiki/Main_Page and have enough of the page hidden so that scrollbars are necessary
(2) Scroll slightly and then immediately move the mouse

What is the expected result?
The scrollbar stays visible while the mouse is moving

What happens instead?
The scrollbar disappears