Reflection Vector not translating into ES2 when applied via an Emissive Color

When you have a Reflection Vector plugged into a Cubemap and applied to the Emissive Channel of an Unlit Material, the Cubemap will not render on a mobile device with ES2 or in ES2 (Mobile/HTML) Preview.

Also Reproduced in Main Promotable CL-2568226

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1. Open QAGame Editor
2. Create a New Opaque Unlit Material
3. Add a Texture Cube Parameter with TextureCube'/Engine/MapTemplates/Sky/SunsetAmbientCubemap.SunsetAmbientCubemap' assigned to it
4. Attach a Reflection Vector WS to the Cube's UV Input
5. Compile and Save Material
6. Add a Sphere in the Level
7. Assign the New Material to the Sphere
8. In Settings, Change the Preview Rendering Level to Mobile / HTML5

RESULTS: Cubemap is not rendered on Sphere

EXPECTED: Cubemap should be rendered on Sphere

MaterialExpressionReflectionVectorWS does not function when used with a cube map on ES2 level devices (or preview mode).