Not sure if that’s an actual bug, but the arm_2jnt_04 seems to have some twist vector issues.
While rigging provided model I went into issues like that:
Hands are not aligned into a neutral pose, so that’s why wrist orient would be handy. The default model is A-pose with hands front (thumbs up). I know there are always limits, so will find another solution for that, but did a quick test with same range of motion with and without wrist alignment, please take a look.