Materials using Landscape Layer Blend are black

When applying a Landscape Layer Blend of textures to the Material Base Color, the preview does not update or shows black instead of how the material is supposed to look. When you disconnect the layer blend and attach a single texture sample, click apply and save then the material updates in both preview and in level. when the texture is directly connected to the base color of the material the log shows:

Display: Validating Material <path to Material>

This is NOT a regression as the issue also happens in 4.27.2

1. Create New Material
   • right click in Content Browser and select Material
2. Create new Landscape with new Material matched.
   • Go to Mode drop down and select Landscape
   • Add your material to the new Landscape
   • Click Create
3. Change mode back to select
4. Open Material
5. Right click in graph and add LandscapeLayerBlend node
6. Add at least one layer to blend mode
7. Right click in graph and add TextureSample
8. Pick a texture for the sample
9. Connect texture to Layer 1 of layer Blend
10. Connect LayerBlend to Base Color of Material
11. Apply and Save

Result: Preview and Landscape shows material as black instead of how it is supposed to look

1. change the connection of the TextureSample RGB to go to Base Color of the material so it bypasses the LayerBlend.
2. Apply and save

Result: Preview and Landscape shows material as should be.

Expected result:  Preview and Landscape shows updated material with new layer blend of textures applied

Actual result:  The preview and landscape (after apply) show up as black and the log has entry:

Display: Missing cached shadermap for Preview:MyMaterial in PCD3D_SM5, Default, SM5