It’s based directly off the Landscape example, just with another two textures, one of which has a real roughness and split-apart height texture. (Which I should probably merge into the base and normal just to save on texture lookups, but haven’t yet.)
I was able to retrieve the actual build errors and it was complaining about more than 16 texture samplers. By my count this is doable with 12, which is within limits, but I’m assuming the engine is doing some magic stuff in the background that require a few more.
That said, “stats” tells me it’s using five texture samplers, which is completely impossible for any interesting mixing - I’m assuming that it is assuming the “soil” layer is at full opacity, which lets it optimize away essentially the entire shader. In this one case.