Artifacts when using virtual textures for multiple attributes in material layers

When using the Material Layer system and virtual textures, the number of physical texture samples in the shader increases with the number of material attributes that a virtual texture writes to. The texture samples are not deduplicated across attribute compilation.

This can further lead to multiple page table samples, since we can only store 8 physical texture indirections per page table.

All of this is bad for performance.

But then there appears to be another issue that with multiple page tables we sometimes see blocky artifacts in texture space. This seems to be worse if we disable Allow Static Lighting in the project rendering settings.

Load the attached project in the editor.
Spin the camera around the sphere in the default map, and observe that blocky artefacts start to appear.
They also appear in the preview window for the material instance on the sphere.