When the mouse pointer is just about 1 or 2 cm above the yellow line the hover doesn't show up.
Steps to reproduce
- Go to a page showing revisions (e.g. https://www.mediawiki.org/w/index.php?diff=2446749&oldid=2428873&title=Extension%3AFlow&type=revision)
- Move the mouse to the left side of the screen (out of the revision slider area)
- Move the mouse vertically 1 or 2 cm above the yellow revision line
- Move the mouse horizontally between different revisions.
The popup showing revision data shows up.
Nothing is shown.
Note: Moving the mouse a bit higher in the revision "bar" area will result in the popup showing up, but this is not intuitive.