I had encountered this bug long ago, but thought it was due to a resource pack I had, so I had deleted it, but I find that it is not caused by addons or packs of any kind. I also find that it can also be activated without dying, as that was the case in the world I had found it in. I cannot put steps to reproduce, unfortunately, as I cannot find how to reproduce this, although I have been trying to. It causes the player's arms to act like they are always drawing a bow, whether holding a sword, a pickaxe, even nothing. And it seems to change on how easily it is fixed. I managed to somehow fix it this time just by exiting the app without closing it and coming back to focus it again. I was using a texture-only resource pack in the image, and I cropped it for easier seeing, but it was not only on the paper doll, but also on the inventory screen as well, and in 3rd person. Though I found that not even an animation/changing resource pack will affect its cause or it even occuring.