Map won't complete despite killing all enemies

I fully cleared the map, but it never gave me the "Map Complete" popup and it doesn't show in the top right that the map is complete. It also doesn't show as complete on the Atlas map and I didn't unlock any surrounding nodes.

I don't remember actually encountering any rare enemies on the map, so maybe there is a small chance for no rares to spawn and the map therefore being impossible to complete.

Image for reference:
https://gyazo.com/f4ef4f6080dc6ac3ee6032e08f837532