flappy wrists

I had a similiar issue. In my case it was due to alternate hands that held things (like a briefcase) and extended the length of the arm mesh.  

I fixed it by making the object independent from the hand/arm.

It could be useful to see the rigging hierarchy for the arms and hands. I was wondering if related to the position of sticks and draggers.

I have seen similar when there is something about the puppet where the rotation of the hands was blocked. In my case, I was using MIDI devices to control a Transform behavior on the hand. (!!) If you watch its like when moving the hand rotation won’t occur - when you stop, the try to straighten. I would check for things like dragger on the wrong layer or similar.

Do you use the IK ARm behavior? I noticed the elbow joint went the wrong way at one stage. You might try putting that on and see if it helps with hands as well.