Instances with close to or over 1000 repositories may consume large amounts of browser memory and cause non-responsive UI when scrolling, filtering, or resizing the browser window while viewing the Administration -> Repositories list.
Additional factors which may contribute are a large number of default realm users. ( in one case 839 users )
At the same time, builds against those repositories may perform adequately.
Administering repositories in an instance with over a thousand repositories should be possible with a responsive UI experience.