Download + launch the licensee repro from here - [Link Removed]
Licensee also described the repro steps, but I was unable to generate the error by duplicating this, however hopefully it gives more insight into where the issue is coming from:
- enable "Generate Mesh Distance Fields" in project settings.
- insert a directional light source, make it dynamic.
- insert a skylight, make it dynamic and assign a cubemap source.
- insert a configuration of 4 static meshes boxes forming a floor, walls and a roof.
- insert a landscape through the middle of the static meshes.
- assign a material to the landscape that uses the "Landscape Visibility Mask" connected to the Opacity Mask in a "Blend Mode=Masked" material.
- paint the landscape invisible inside the static mesh configuration.
- observe that there are no artifacts in editor (top part of image).
- package the project (i.e. cook the level for windows) and run the cooked game binary - observe artifacts on the walls of the static mesh configuration (bottom part of image).