There are a number of known issues with the skeletal system and location of hands - we have done extensive testing and found the OrbBec SDK way to unreliable for any sort of commercial work.
You might want to have a look at the Nuitrack SDK which we have found can produce better results. BUT even it too has issues with stability of the hand joints once they hands are in front of the body.
Seems like all the SDK developers think that T poses and star jumps are all we are looking to track = when the most common body poses for interaction are with the HANDS in front of the body. Something that all the current crop of SDK seem to fail at.
Whoever gets that 100% working wins our custom fwiw.