Yes, the glTF loader routines inside the simple OptiX SDK examples are not supporting all features allowed by the glTF specifications.
Please see this thread for explanations of some of the limitations:
https://forums.developer.nvidia.com/t/vtk-optix-triangle-mesh-write-read-operations/293966/2
I would need to debug into what happens with the biplane and woman models.
(My GLTF_renderer example can load these without problems.)