A few issues with Polybrush and custom Shaders

I am using the latest Polybrush 1.01 and noticed a few issues-

Vertex Color painted meshes flicker or do not work when Instancing is enabled on the material and Apply as is set to "Additional Vertex Streams". Do I need to do anything else in my shader to get Polybrush to work with Instancing?

I am getting the warning "It doesn't look like any of the materials on this object support vertex colors!", even though my material absolutely does support vertex colors and it works fine with Instancing off. What exactly is Polybrush looking for?

I am using the built-in pipeline on Unity 2020.1.0b11