The fact that your second one works and the first one doesn’t points to it not being an issue with the rig code, but most likely a skinning issue, or attributes not being set properly.
Here is a quick video I put together going over the attributes and settings for the dynamics:
I think once you watch that and try some of the steps in there, you should be able to get it working. If it still doesn’t work, I’d check to make sure the mesh is skinned to the bone.