VertexInterpolator Makes Landscape Materials Fail to Compile

If a VertexInterpolator is used in a material that is applied to a landscape the material will fail to compile.

Found in 4.20 CL# 4369336, 4.21 CL# 4.21 CL# 4613538, 4.22 CL# 4681912

1. Open the editor
2. Create a landscape material using a VertexInterpolator node
3. Apply the material to the landscape

Steps with project:

1. Open "NewMap"
2. Goto Window>Developer Tools>Output Log
3. Open the Output Log

Results:
The landscape material will fail to compile and revert to the default material 

Expected:
The material would compile and appear on the landscape