Terrain totally black after adding materials
Hello. I’ve just bought this product and I got a big trouble. 
My simple goal is to create a map from scratch, so I do exactly the same simple steps of the
The problem is the following: when I add the material the surface is totally black, both when I use the instance material “forest-ground-snow-ice-weighted” and when I use the “forest-ground-rocks-mud-grass”.
I’ve also tried to rebuild to light several times, or adding sky light and spheres or stuff like that, but nothing changed.
It’s pretty weird because all other materials work fine, even those contained in the package. The problem applies also for the two master materials.
The version of Unreal I’m using are 4.16.2 and 4.15.3.
I also tried to add one more landscape to the example map provided with the package, but the problem still remains.
But, if I change the material to the landscapes already placed in the map, it works.
It’s very frustrating being stucked in this way.
How can I solve this problem?
Thank you in advance!