Black flickering on Mesh particles when set to a non-default Facing Mode or using Orient Mesh to Vector and when using Particle Position in the Material's World Position Offset

Steps to Reproduce

Quick Repro

  1. Open the attached project
  2. Open FX_Emitter_System
    1. This project was provided by a public user, but I've rerouted Particles Position directly into World Position Offset in the Material (M_VertexAnim) for a simpler repro
    2. The issue is visible in the level, but it's less obvious

Manual Repro 1

  1. Open a project
  2. Create and open a new Material
    1. Set Base Color to some non-black color
    2. Place a Particle Position node in the graph and connect it to World Position Offset
  3. Create and open a Hanging Particulates System
  4. Add a Mesh Renderer to the Emitter
  5. Set the Mesh Renderer's Particle Mesh to Cube (/Engine/EngineMeshes)
  6. Enable Override Materials and add an element to the array
  7. Set the Override Material's Explicit Mat to your material
  8. Set the Facing Mode to Velocity, Camera Position, or Camera Plane
  9. View the System in the Preview Viewport or Level Viewport

Manual Repro 2

  1. Do steps 1-7 from above
  2. Add the Orient Mesh to Vector module to Particle Spawn or Particle Update

Result: The particles have black flickering

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ComponentRendering - Niagara
Affects Versions4.25
Target Fix4.26
CreatedJul 23, 2020
UpdatedJul 27, 2020