High priority @Geez
This goes along with the weapon switching animation bugs, where the IK poses become a mess after switching weapons using the hotbar (from one weapon holstered to another into your hands?) while standing or moving.

it might be reproducible that way? but not sure. I believe it's to do with client-server synchronization since the person wielding the gun does not notice that he has nothing in his hands.

Refer to T139814
for the IK issues. (especially disable the UAction of Jumping while in the raised weapon state, to stop the major issues like these arising)