Hi gooner, that's pretty strange looking. If it only happens when you apply a unit change my first guess that it's some kind of bug in 3ds Max's scaling mechanism.

Is it possible that your object is unusually large or small in unit size after the scaling is done? Like does it have number values very small like 0.0000001 units across or very large like 100000000000000.0 units across the entire object? Or is the object located very far away from the 0,0,0 origin point? If so then maybe you are running into numeric precision issues related to using numbers with very large or very small values.

Can you export out one of the damaged versions from 3ds Max in either .fbx or .obj format and attach it here or in a file sharing service so I can try to see the nature of the damage? If you can repeat it with just one small piece that would be best.

- Michael

Hi Michael, thanks for your help. I had to tweek the model so I then did the import/export (as ngons) again with the correct units in place, it worked fine and I don't have any shading issues. I will try to replicate it and let you know exactly what I've done