There is no way to scroll through members page
It just shows the first page...
Could you please say, how many members you see in Dashboard > Forums > Members admin page? Do you see all 254 users there?
No.. that page is messed up as well.. unless I search.. then I see them all. See this post: https://wpforo.com/community/qa-layout-bug-reports/members-in-the-dashboard-only-shows-first-screen-of-list-you-have-to-search-to-show-all-of-them/#post-48
This has been fixed in the dashboard area and on the front-end