Volumetric Fog visible rectangle artifact on Play (Temporal accumulation artifact)

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Hi everyone,

Screenshot 2026-07-24 085452
Screenshot 2026-07-24 0854521920×1079 93.6 KB

When I hit Play (PIE), a visible inner rectangle appears in the center of the screen with slightly different lighting/fog, which then gradually fades out over the first couple of seconds.

I isolated the issue and confirmed that disabling Volumetric Fog on my ExponentialHeightFog completely removes the artifact.

  • My PostProcessVolume has Infinite Extent (Unbound) enabled.

  • Exposure is fixed (Min/Max EV100 set to the same value).

  • Camera Constrain Aspect Ratio is turned off.

It looks like a temporal accumulation / initial grid warm-up issue with the volumetric fog frustum.

Aside from using a camera fade-in on BeginPlay to hide the warm-up frames, is there an engine setting, console variable (cvar), or volumetric fog parameter (like grid sizing/warmup) to prevent this initial rectangular frame artifact from rendering at start?

Thanks in advance for any advice!