@Deltakosh… I validated the file in the SandBox (don’t know why I didn’t think to do that sooner), it appears to be valid with no errors. I’m using the viewer in my webapp for this model and for models which work okay.
The console doesn’t throw any errors when rendering the scene, perhaps I’m missing an albedo or alpha setting somewhere? I appreciate your help as always - I thought I was in the last few hours of this project but I guess that’s how it goes 
