@Pavanpk the new models are being loaded, it’s just that (at least in the case of New_6x6.glb) they’re far away from the target of the camera (origin 0, 0, 0) and therefore out of frame. If you load the models into Blender you can check:
You see different results in the Sandbox because it automatically moves the camera to nicely frame whatever meshes have been loaded.
When you open the Inspector in Sandbox you can see how the camera target and radius have been automatically changed to frame the mesh:
