When people choose other revisions in the revision slider, parts of the page, but not all is reloaded. Gadgets listening only to a page reload, but not to the diff changing do not work anymore after the change. The example we know of so far is the Wikeddiff gadget. As long as it does not listen to the diff changing, it does not work well together with the revision slider.
Adapt User:Cacycle/wikEdDiff.js to use the diff-refresh hook as described in T143199#2631963
Since this is the original gadget, this is the one we fix.
The revision slider is a feature that adds a visualization of all revisions to the compare screen. Revisions are represented as bars on a line and can be selected using two pointers. 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