Sorry this one is beyond my skill level perhaps you would be better off asking this in the thread you started about this issue Animations lost when exported with GLTF2Export.GLBAsync and ping bghgary.
When you say you exported and downloaded the alien file I am not sure how you did that, you can find the full alien folder here Babylon.js/Playground/scenes at master · BabylonJS/Babylon.js · GitHub
If you downloaded from here and you checked all the relevant files were saved it wasn’t working then I go back to my first suggestion.