Yeah, the hrank and lrank searches are broken for some ranks https://forum.inaturalist.org/t/rank-filters-sometimes-show-wrong-results/97
@shauns if you just want to see all the hybrid taxa observations in South Africa, you can use the search URL modifier rank=hybrid right on the normal website without using the API. There are a lot of search filters that aren’t available for use in collection projects.
https://www.inaturalist.org/observations?place_id=6986&rank=hybrid&verifiable=any&view=species