I also struggled getting something like this to work. I involved Texture Graphs, Geometry Scripts, and PCG Graphs in one blueprint 
The idea was to use the texture graph to create a heightmap to build a landscape, then use PCG to populate the landscape.
Setting up my PCG nodes, I got the debug boxes to stick on my landscape!
The key for me was to create a ‘PCG World Actor’
The landscape in question.
