UE 5.7 – Substrate + Clear Coat + Lumen HWRT causes colorfill square artifact

Development Rendering
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1

II’m experiencing a rendering artifact in UE 5.7 that I can’t resolve.

Setup:

  • Substrate material with Clear Coat layer

  • Lumen Hardware Ray Tracing reflections enabled

  • “Max Roughness to Trace” set to anything other than 0.2 (e.g., 0.4, 0.6, 0.8)

Issue:
A small colorfill square / tile artifact appears on screen. It stays fixed in the same place (not moving with geometry). Disabling Hardware Ray Tracing makes it disappear. Switching reflections to Screen Space turns the square black.

What I’ve tried (none worked):

  • Updated the BIOS of my Motherboard

  • Updated NVIDIA driver to latest

  • Deleted Intermediate, Saved, DerivedDataCache

  • Tried console variables:

    • r.Lumen.Reflections.MaxRoughnessToTraceClamp 0

    • r.Lumen.Reflections.Temporal.NeighborhoodClampScale 0

    • r.Lumen.Reflections.SamplePerPixel 1

    • r.Lumen.Reflections.SpatialFilter 0

    • r.Lumen.Reflections.RadianceCache 0

    • r.LumenScene.Radiosity.ProbeSpacing 2

    • r.raytracing.nanite.mode 1

  • The artifact remains. Only setting r.Lumen.Reflections.Temporal 0 changes it from a square to a bloom flare (not a fix).

Question:
Is this a known Substrate + Clear Coat + Lumen HWRT bug in 5.7? Are there any working workarounds besides disabling Substrate or lowering Max Roughness?

Thanks for any help.

Screenshot 2026-04-17 053440
Screenshot 2026-04-17 053440907×634 89.7 KB

Screenshot 2026-04-17 053927
Screenshot 2026-04-17 0539271050×871 191 KB

2

Hi !
I happen to have the same exact issue but i didn’t dig in as deep as you did. I did find that Max roughness to trace changed it and i do have HWRT and substrate so we must experience the exact same issue.

As for a solution, well it’s in fact pretty easy to overcome ! I use 5% overscan and that is enough to make it go away. I’m rendering so i just added an extra node in my movie render graph, but i’m pretty sure you can do it at runtime with a cinecamera.

But this does need to be looked at. Did you open a bug report ?

3

Experiencing the exact same thing. Let’s hope this gets fixed for 5.8.

4

Hi Allan. I had the same issue, I have the “same” setup that you have too. What I found that worked for me was actually to add / remove a CVAR.
r.Lumen.Reflections.maxRoughnessToTrace -1

This took away the entire bug for me and I will flag this to Epic as well. I really hope this helps you out, let me know.

Kind regards, C