I've never downloaded any mods before, nor have I played on this map prior. For some reason, I am unable to complete the "Desert Shield" mission as a horde is not spawning in Salmiya, or any other town of a similar name.

The only thing that could have possibly affected this is that I completed other quests and unlocked this mission before finishing "Hydrate or Die-drate", though I don't see why this would lock away that quest.

Is there any way to fix this?