DrawScale = Landscape->GetRootComponent()->GetRelativeScale3D();
DrawScale = Landscape->GetActorScale3D();
Changing as above will solve the problem.
1. open NewWorld.umap
2. change the scale of the Cube
3. change the Grass Density of NewLandscapeGrassType.
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-102930 in the post.