Problem:
Lights in avatars always affect for MirrorReflection layer regardless of its culling mask configuration.
How to reproduce:
I prepared a world to test the behavior.
In this world, some spheres belong to different layers in the following layout.
First row (left to right):
  • Default
  • TransparentFX
  • Ignore Raycast
  • Water
  • UI
Second row (left to right):
  • Interactive
  • Player
  • PlayerLocal
  • Environment
  • UiMenu
  • Pickup
  • PickupNoEnvironment
  • StereoLeft
Third row (left to right):
  • StereoRight
  • Walkthrough
  • MirrorReflection
  • reserved2
  • reserved3
  • reserved4
Also, this world has a camera at back to observe MirrorReflection layer.
I changed into an avatar that has a directional light only for UI layer. (Please see 1st image for avatar details.)
I think that it should affect only a sphere in UI layer. However, it affects for MirrorReflection layer too like 2nd image.
Environment:
  • VRChat Build 1172
  • VRCSDK3-AVATAR-2022.02.16.19.13_Public