If you use the Location search instead of the Place search, iNat won’t find the province because there’s a bug with names that are too long. Unfortunately, the bug probably won’t be fixed until the entire Explore page is rewritten, so until then, please use Filters->More filters->Place
(if you’re interested in the details of the bug, please see https://forum.inaturalist.org/t/boundaries-of-the-northwest-territories/40001/4)