In the attached file, usdskel_noanim.usda.zip, the SkelAnimation prim does not have any of the rotations, translations or scales attributes authored.

The expected behaviour here is to use the skeleton's restTransforms, but with USDIMAGINGGL_ENGINE_ENABLE_SCENE_INDEX=1 the skinned geometry does not appear. In Hydra 1, or when using the Bake Skinning utility, the geometry is skinned as expected using the rest transforms.