If the arm is Warp Independent, then yes it's on a different mesh as other parts and shielded from any warping that might happen there.
Can you select the topmost row on the left side of the Puppet panel (i.e., so no layer is selected, only that header) and see if the origin for the puppet has any Draggable handle tag on it? If not, select the topmost layer, and check its origin.
I'm assuming if you disable the Draggable behavior (i.e., turn off its eyeball), the problem goes away?
Feel free to send me a shared link to the .puppet file via private message if you'd like me to try to reproduce the issue. Thanks.
Simple enough! Deselecting from the character revealed a Draggable handle in that area, I deleted it and put a new one on the Hand, works as it should. Thanks.