Version 1.3.4
After regeneration I get stuck in the pose, but the outer skin does not (if that makes sense?).
In the screenshot you can see a brown sleeve (from my outer skin) along both sides of the body. Those sleeves just function like arms now while the arms themselves are stuck in the cross pose.

Could you indicate what other mods you have installed?

Yes, sorry.

https://pastebin.com/VBEW4eHi

I will investigate this a lot further when I am I am home, unless one of the other collaborators does it first

Do you know if any of these mods change the way the player is rendered or render something in the player at all?

The only two mods I can think of of the top of my head would be Tool belt and Cosmetic armour.

Edit: Oh, and perhaps Backpacks?

Thank you