Grotto Caves Horde Missing

[Astral Empyrean]

I'm at the end game. But the Grotto Caves Horde doesn't show up on the map or the Horde Exterminator list. But it does show up as uncompleted in the incomplete portion of the exterminator list. I've tried saving the game and loading, checking all the know areas at different times. But it just will not spawn. And running around the area doesn't trigger horde music either. It's annoying because I can't complete the cascades.

[simon.pete15]

Go out of that area completely. If there's a job to do in another area, go there and do it. Then come back into the area the Grotto Caves are in. This forces the area to be reloaded, which should get this hoard to respawn.
It's also possible that you've killed off this hoard, but 1 or 2 freakers are still loose in the area. You'll have to find and kill them. Sometimes a freaker can get stuck in an inaccessible spot. Getting the area to reload will probably release it.