[As described on: https://www.mediawiki.org/wiki/Topic:Tmxhqv9cpkrpfb25 and mostly verbatim taken from it]

Problems:

• As a user, I can't easily use revision slider without clicking the "diff" link while on the history page.
• As new user, it is not completely obvious how to get to the revision slider.
  • The entry point unclear - Presumably, this would appear in the history page, but only shows up when a "diff" is clicked.

"Despite knowing of the existence of revision slider it was unclear how to get to it. In fact it made me think that it didn't work in certain namespaces after going through multiple page histories because I had forgotten that "diff" must be clicked."

Possible solutions
There might be a user setting to decide where the revision slider is is situated. See this discussion on en Village pump