This only happens when

1) Hair Width is very small. e.g. 0.01 in the example

2) Light has raytraced shadow and Samples Per Pixel has a value > 1. e.g. 8 in the example

The problem seems to be related with rasterization. r.HairStrands.RasterizationScale 0 workarounds ** it. If this is by design, it would be very helpful to reflect the parameter in the UI.

Steps to Reproduce

Open attached project to reproduce

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There's no existing public thread on this issue, so head over toAnswerHub just mention UE-94065 in the post.

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ComponentRendering - Ray Tracing
Affects Versions4.25
Target Fix4.26
CreatedJun 8, 2020
UpdatedJun 29, 2020