Description

When custom instance data is used to calculate WPO in a Material and applied to an ISM the WPO value in the Lumen scene (ray tracing scene) is different than the visible scene resulting in incorrect shading and shadow-like artifacts.

Steps to Reproduce

1. Download the attached project and open the Issue level
2. Enable r.RayTracing.Geometry.InstancedStaticMeshes.EvaluateWPO 1
3. Enable the Lumen scene visualization mode

Expected

The mesh in the ray tracing and Lumen scene is the same as the visible mesh

Actual

The mesh in the ray tracing and Lumen scene seems to follow the behavior of the first instance instead of taking into account the custom instance data. This also appears to be the case if PerInstanceRandom is used.

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Unresolved
CreatedSep 19, 2025
UpdatedSep 19, 2025
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