workaround metal/amd regression since 2018.1, investigation still in progress

com.unity.render-pipelines.high-definition/HDRP/Material/Lit/Lit.hlsl

     float iblMipLevel;
     // TODO: We need to match the PerceptualRoughnessToMipmapLevel formula for planar, so we don't do this test (which is specific to our current lightloop)
     // Specific case for Texture2Ds, their convolution is a gaussian one and not a GGX one - So we use another roughness mip mapping.
+#if !defined(SHADER_API_METAL)
     if (IsEnvIndexTexture2D(lightData.envIndex))
     {
         // Empirical remapping
+#endif
     {
         iblMipLevel = PerceptualRoughnessToMipmapLevel(preLightData.iblPerceptualRoughness);
     }