UE 5.8 DX12 Rendering Regression on GTX 1660 Series – Missing Shadows with MegaLights

Development Programming & Scripting
,
1

Engine Version: UE 5.8
Platform: Windows (Packaged Builds)
Graphics API: DX12
Feature Set: MegaLights, Lumen, Virtual Shadow Maps, SM6
Hardware Affected: Confirmed on GTX 1660 Ti and GTX 1660 Super
Severity: High (scene lighting appears visually broken)

Summary

After upgrading our project from UE 5.7 to UE 5.8, a subset of players are experiencing a rendering issue where:

  • Shadows disappear completely.
  • Overall scene contrast is significantly reduced.
  • Issue affects all maps, including the main menu map.
  • Issue is only present under DX12.
  • Launching the game with -dx11 completely fixes the problem.

The issue is reproducible on at least two separate user systems with GTX 1660-class GPUs.

Visual Symptoms

Affected users report:

  • Missing shadows throughout the scene.
  • Bushes and trees appear washed out and self-illuminated.
  • Increasing graphics settings does not restore shadows.
  • Main menu environment exhibits the same problem.

The scene appears correctly lit under DX11.

Hardware Confirmed Affected

User 1

  • NVIDIA GTX 1660 Super (6 GB)
  • Intel i5-9600K
  • 32 GB RAM

User 2

  • NVIDIA GTX 1660 Ti (6 GB)
  • Intel i7 (6C/12T)
  • 32 GB RAM

Additional Information

DxDiag from one affected user shows:

  • Windows 10 22H2 (Build 19045)
  • WDDM 2.7
  • DirectX 12
  • Latest NVIDIA driver available at time of testing

Current Renderer Configuration

r.MegaLights.EnableForProject=True

r.Shadow.Virtual.Enable=1

r.RayTracing=True

r.RayTracing.Shadows=False

r.Lumen.HardwareRayTracing=False

Target Shader Formats

+D3D12TargetedShaderFormats=PCD3D_SM6

Project uses:

  • DX12
  • Shader Model 6
  • Lumen
  • Virtual Shadow Maps
  • MegaLights

Nanite is disabled.

Regression Information

UE 5.7

Rendering behaved correctly.

Key settings:
r.Shadow.Virtual.Enable=1

r.RayTracing.Shadows=False

UE 5.8

Issue appears after upgrade.

Several renderer configurations were tested (see below) with no success.

Troubleshooting Performed:

Shader Rebuild

  • Implemented a shader compilation screen to force recompilation.
  • Tested with: -clearPSODriverCache
  • Result: no change

Clear GPU Shader Cache

Tested on affected systems. No change.

Update GPU Drivers

Affected users updated NVIDIA drivers. No change.

Re-enable Virtual Shadow Maps

Restored: r.Shadow.Virtual.Enable=1
No change.

Show more lines

Disable Ray Traced Shadows

Tested with r.RayTracing.Shadows=False
No change.

Show more lines

Critical Discovery

Launching the exact same packaged build using: -dx11

completely resolves the issue.

Under DX11:

  • Shadows render correctly.
  • Foliage appears normal.
  • Overall lighting matches expected visuals.

Under DX12:

  • Shadows disappear.
  • Foliage becomes overbright.
  • Scene lighting appears incorrect.

This strongly suggests a DX12-specific rendering path issue.

Reproduction Steps

  1. Create/open project using:

    • UE 5.8
    • DX12
    • SM6
    • MegaLights enabled
    • Lumen enabled
    • Virtual Shadow Maps enabled

  2. Package for Windows.

  3. Run on a GTX 1660 Ti or GTX 1660 Super system.

  4. Observe:

    • Missing shadows
    • Overbright foliage
    • Flattened lighting

  5. Relaunch same build with: -dx11

    Observe:

    • Shadows restored
    • Foliage renders correctly
    • Lighting appears normal

Expected Result

Under DX12:

  • Shadows render correctly.
  • Foliage receives proper shadowing.
  • Visual output matches DX11 and UE 5.7.

Actual Result

Under DX12 on affected GTX 1660 systems:

  • Shadows disappear.
  • Foliage appears excessively bright.
  • Scene lighting is significantly altered.

Under DX11:

  • Rendering behaves correctly.

Questions

  1. Is there a known UE 5.8 regression involving:

    • DX12
    • SM6
    • MegaLights
    • Virtual Shadow Maps
    • GTX 16-series (non-RTX Turing) hardware?

  2. Are there known differences in the DX12 rendering path for GTX 1660-class GPUs versus RTX hardware when MegaLights are enabled?

  3. Is there any known issue with UE 5.8’s SM6 path on GTX 1660 Ti / GTX 1660 Super hardware that could produce missing shadow evaluation while leaving direct lighting intact?

Any assistance or guidance would be greatly appreciated. This issue did not occur in the UE 5.7 version of the project and currently appears limited to DX12 rendering on specific hardware.