I don't know why it is doing that. It's not our viewer.
We didn't write the viewer; we only provide what it needs to run inside of Opus, the same as it runs inside of File Explorer.
From 3D Object preview (3mf, fbx, glb, gltf, obj, ply, stl) :
That's assuming it's the Windows 3D Object viewer that you're using. If it's an entirely different viewer than I know even less about it. Either way, we're the wrong people to ask; you need to ask the people who wrote the viewer/component in question.