I'm using Unity 2018.1.0f2 with ProBuilder 3.0.8 from the package manager. My workflow is that I have a separate ProBuilder scene where I construct my meshes and than use "Tools → ProBuilder → Export → Export Asset" to create a prefab. Back in my proper game scene I noticed that despite generating UV2s I'm getting "This GameObject has overlapping UVs" warnings in the inspector. Looking at the baked lightmap everything seems to be using the UV1 layout. Going back to my ProBuilder scene the UV2 is missing. It seems to get deleted when I export. Is there a technical reason for this or am I doing/understanding something wrong here?