How are you calling those functions? Did you wrap the fog actor in a blueprint and call from the construction script and/or BeginPlay event? It will need to run the precompute after the actor is spawned and “in level” so construction script probably wont work. This might seem obvious but depending how you have it set up it could be running the precompute too early.
I would also recommend setting all of the other variables to default values erither manually or in a blueprint (these can be changed after precompute), as I had a similar issue where the defaults were not being used, forcing all variable values to 0 instead.
Also how are you controlling the spawning of this actor? Is this in a level blueprint or spawned by another actor?