UE5 Mobile Deferred – Subsurface Shading Mode disabled when r.AllowStaticLighting=True with dynamic lights

Development Rendering
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1

Why does enabling r.AllowStaticLighting on mobile with deferred rendering cause Subsurface Shading Mode to stop working, even when all lights are dynamic?

Is this a design limitation, or could it be a bug?

2

重现步骤
Description：

I’m working with UE5 on mobile using the deferred rendering pipeline. In my scene, all lights are dynamic. However, I’ve noticed an issue:

  • When r.AllowStaticLighting=False, the Subsurface Shading Mode works correctly.
  • When r.AllowStaticLighting=True, the Subsurface Shading Mode stops working (it looks completely disabled), even though there are no static lights in the scene and all lighting is dynamic.

Reproduction Steps：

  1. Create a project with UE5 targeting mobile (deferred rendering).
  2. Place a mesh with a material that uses Subsurface Shading Mode.
  3. Add only dynamic lights in the scene (no baked/static lighting).
  4. Toggle the console variable r.AllowStaticLighting between False and True.

Actual Result：

  • When r.AllowStaticLighting=True, Subsurface Scattering (SSS) stops working.

Expected Result：

  • Subsurface Shading Mode should still function with dynamic lights, regardless of the value of r.AllowStaticLighting, since no static lighting is being used.
3

Hi Xiao,

This is most likely a bug as there’s on clear reason why the two shouldn’t coexist. Can you attach a repro case so we can diagnose the issue?

Best regards.