a similar issue was previously noted here: https://forum.inaturalist.org/t/user-with-many-species-is-excluded-from-stats-if-not-within-top-200-observers-in-traditional-project/42912
since the page is broken, i made a page to display the results of the associated API requests in a more human-friendly format. this should allow you to see observers by species count. however, it should be noted that the API won’t return results beyond the top 500 observers.
page: https://jumear.github.io/stirfry/iNatAPIv1_observations_observers
code: https://github.com/jumear/stirfry/blob/gh-pages/iNatAPIv1_observations_observers.html
example use: https://jumear.github.io/stirfry/iNatAPIv1_observations_observers?year=2023&order_by=species_count