Hi second-prior,
As mentioned here:
https://cineversity.forums.maxon.net/topic/799/ik-rig-question?_=1701325135852
My tip would be to bind the joint with a little angle left if the arm is stretched. This way, you avoid the "kind of" Euler Angle behavior.
I need a file with the joint setup. I don't need the character if you don't want to share it.
Files as c4d can be 1MB for the forum
Otherwise, please use Dropbox, Google, Apple, Adobe, or Wetransfer as cloud services.
All the best