I set up a documentation site using the RTFM skeleton and my user started adding pages. For some reason the prev/next page arrows are no longer working. If you click them nothing happens. The page/folder structure appears to be correct. He is adding content via the admin plugin.
Hard to tell. The example sites work fine, and also http://learn.getgrav.org/. Try inspecting with the browser inspector and comparing the markup. Maybe some element is over preventing the mouse to actually click them.
Would need to get a copy of your site to really tell what’s going on. You can ZIP it up and PM the link to download it.