When you hover quickly over the revision bars, the tooltip moves with the mouse. The grey rectangle that connects the tooltip to the corresponding bar, however, disappears.
Let the grey rectangle connect the tooltip and the revision also when hovering quickly.
This is part of adding the revision slider to the revision diff page. The revision slider is a feature that adds a visualization of all revisions to the compare screen.
The revision slider was originally prototyped by the WMF Community Tech team and then handed over to the WMDE TCB team, as it is also a solution to fulfill a wish of the German Community Wishlist: https://de.wikipedia.org/wiki/Wikipedia:Umfragen/Technische_W%C3%BCnsche_2015/Artikel#Anzeige_aller_Bearbeitungskommentare_im_Diff