Landscape Actors are rendered differently than Static Meshes which is what the guy is using in that video so even though they are both comprised triangles the way those triangles are rendered is different which causes issues - That’s why i had to create a tessellated displacement material just for Landscape Actors because the standard method used for Static Meshes would not work.
The last time i tested World to Tangent on Landscape Actors was in 4.5 so Epic may have fixed the issue since then, i know they have increased the sampler limit so i may be able to add more layers as well.