When you mirror instanced / referenced geometry in 3DS Max then export it using the latest 3DS Max exporter to gLTF, the mirrored geometry in Babylon appears with backwards facing normals while the source geometry has visually correct normals.
It sort of makes sense in that when you use Max’s mirror feature it basically just applies a -1 scale, which sort of would turn the geometry inside out. The fix may be tough as this may be as much of a modeling technique / 3Dsmax issue as an exporter issue, but I figured I would report it anyway.
I am using Max 2019 with latest Exporter.
