[abenedik]

I understand now - you wanted to provide a texture that would represent transparency.

This is not supported by the PBR shader in DXEngine.
If you check the description of the Transparency value in the TextureMapTypes enum, you will see that it is written as: "Transparency (not supported)". It is there if you would use that enum for your own shader.

So to use the transparency in the PBR, you will need to bake it into the base color texture's alpha channel (and also have the HasTransparency set to true).