Issue with the shoulders

Hi,

I'm currently busy with the creation of the shoulders. Setting up the "left" shoulder is fine and it move alone.
Although it looks simple, every time I'm creating the "right" shoulder, moving the left shoulder makes both shoulders to move together.

I thought the problem could come from the "symmetrize" function but even recreating the right part manually doesn't solve the problem.

Any thoughts ?

I really appreciate any help you can provide.

Jean-Luc