Nanite + r.RayTracing.Nanite.Mode 1 causes flipped normals in Path Tracing mode (UE 5.7.4)

Development Rendering
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Hi,

I’m encountering a normal flipping issue with Nanite meshes in Path Tracing mode and would appreciate any help.

Environment

  • Unreal Engine 5.7.4

  • Normal maps baked externally, imported as BC5 (DirectX format)

  • All materials are Opaque (no Translucent or Masked materials involved)

Problem

With r.RayTracing.Nanite.Mode 0:

  • Lit mode → Normal display is correct

  • Path Tracing mode → All Nanite meshes appear broken/corrupted

With r.RayTracing.Nanite.Mode 1:

  • Lit mode → Normal display is correct

  • Path Tracing mode → Mesh corruption is resolved, but normals appear flipped

20260412153309
202604121533091284×694 274 KB

20260412153143
202604121531431638×911 413 KB

20260412153113
202604121531131641×923 409 KB

What I’ve tried

  • Enabled Explicit Tangents in Nanite Settings → No effect

  • Enabled Use High Precision Tangent Basis in Build Settings → No effect

  • Changed Position Precision in Nanite Settings (tried multiple values including Auto, 64cm down to 1/8192cm) → No effect

  • Flipping the green channel of the normal map fixes Path Tracing, but then Lit mode becomes flipped instead

Since r.RayTracing.Nanite.Mode 1 successfully resolves the mesh corruption issue in Path Tracing, I would like to keep this setting. However, the flipped normals are preventing me from doing so. Any workaround or fix would be greatly appreciated.

The fact that Lit and Path Tracing read normals in opposite directions with Mode 1 seems like a bug. Is this a known issue in 5.7.4?

Thank you!