When using a material with a translucent blend mode, you can not use the lighting modes "Volumetric PerVertex NonDirectional", or "Volumetric PerVertex Directional" and the Tessellation settings "PN Triangles", or "Flat Tesselation" together. Both lighting modes and tessellation can be used separately but print an error when both are used together. The error that is printed is:

Error [SM5] BasePassTessellationShaders.usf(32,3-25): error X3018: invalid subscript 'AmbientLightingVector'

This issue does not appear to be a regression

Versions tested: Issue occurs in all versions tested
4.16.3 - CL: 3561208
4.17.2 - CL: 3658906
4.18P2 - CL: 3660543

Steps to Reproduce
  1. Create a new project (no template or starter content needed)
  2. Create a new material > name it "NewMat" > open
  3. Set the blend mode to translucent
  4. Set "Lighting mode" to "Volumetric PerVertex NonDirectional", or "Volumetric PerVertex Directional"
  5. Set tesselation mode to "PN Triangles", or "Flat Tesselation".
  6. Compile blueprint
    Result: An error prints and the material will not compile
    Expected Result: The blueprint compiles

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Affects Versions4.
Target Fix4.24
Fix Commit7844634
Main Commit8980992
Release Commit9552237
CreatedOct 3, 2017
ResolvedAug 7, 2019
UpdatedOct 28, 2019