Also, here is the simple workaround. A function change in MaterialTemplate.usf . Line 1739 .
uint DiscardMaterialWithPixelCoverage(FMaterialPixelParameters MaterialParameters, FPixelMaterialInputs PixelMaterialInputs)
{
ClipLODTransition(MaterialParameters);
float OriginalMask = GetMaterialMaskInputRaw(PixelMaterialInputs);
float MaskClip = GetMaterialOpacityMaskClipValue();
if (View.NumSceneColorMSAASamples > 1)
{
MaskClip = MaskClip * 0.05; //Workaround for Alpha2Coverage
float Mask = (OriginalMask - MaskClip) / (1.0 - MaskClip);
uint CurrentPixelCoverage = GetDerivativeCoverageFromMask(Mask);
clip(float(CurrentPixelCoverage) - 0.5);
return CurrentPixelCoverage;
}
clip(OriginalMask - MaskClip);
return 0xF;
}