Here i load a tpose model through asset container and then instantiate it, and then try to load and clone the animation groups from another asset container.
I don’t quite know why it works in 4.2 because an animation loaded from a gltf/glb file must update the transform nodes, not the bones. So you should modify return avatar.skeletons[0].bones[idx]; to return avatar.skeletons[0].bones[idx].getTransformNode();:
No, bones are not transform nodes (they inherit from Node, not TransformNode).
When loading a gltf/glb file, each bone of a skeleton is linked to a TransformNode (bone.getTransformNode() returns a non-null value) and it is this TransformNode which is animated, not the bone (but the bone still gets updated by the TransformNode matrix to mirror the transformation).