Strange. It seems like there's only a set amount of animal herds on the map at a time so if you kill some animals but don't finish off a herd then a new one won't spawn to refresh animals, but I'm not sure why you wouldn't see any unless your path finding and spotting is really bad.

They do have a habit of being in very specific areas of the regions they belong to, but I can't be 100% certain as I don't hunt very often in the first place.

Tks for help. I managed to run into few herds eventually. Just funny that it took me 50+ plus days to do so.