Going a little further, It is important to understand there is the layer hierarchy in the puppet artwork, but there is also a MESH hierarchy. A new mesh is started each time an independent layer is found. (That is what independence does - start a new mesh). Any artwork under a layer that is not independent is included on its parent layer mesh.
Meshes attach to their parent mesh by having some overlapping artwork. Like the arm overlapping the shoulder of the body a bit. With no overlap, it is hard to connect the layers. If an independent layer only has independent children, then the parent mesh is empty - no artwork in it. There is then no,artwork for the children to attach to (nothing to overlap with) so the child do not attach correctly to the parent.
If you turn on the mesh icons at the bottom of the scene panel etc, the yellow outline shows the mesh outline. This gives a hint want is in that mesh.