Tessellation Materials are not working on Landscapes

Tessellation is not working on landscapes, but it does works fine on static meshes. This is a regression from 4.23.1 (CL-9631420) where the tessellation was visible with this setup.

This was tested and reported in 4.24 (CL-10570792) and reproduced in 4.25 (CL-10773962)

1. Open the UE4 Editor and create a Blank project
2. Create a Material with the setup in the screenshot (Constant3Vector, TextureSample, and a Constant. Flat Tessellation needs to be set on the Material.
3. Create a Landscape and apply the material
4. In the Viewport change the Lighting to Wireframe from Lit

Results: The landscape is not showing the tessellation in wireframe mode.

Expected: Landscape should show the tessellation and displacement