Cloning a glTF asset with skinning is not easy right now. There are a bunch of features we added to support glTF like skeleton.overrideMesh and bone.linkTransformNode() which are not cloned and can’t really be cloned easily.
We’re currently thinking about adding a clone method to an AssetContainer: Make sure we can clone an asset container · Issue #6358 · BabylonJS/Babylon.js · GitHub
For now, the best option is to load the glTF multiple times.