What causes picked up ( and attached) weapons to slowly start drifting from socket position?

Yes, always right. And like if you turn the character to face left, it changes position but it is still going Y+. All the weapons are is two things, a static mesh, and a box collision, and everything is set to either ignore (mesh) or overlap (box collision).

Hmm…I could try turning off the animation BP, and then no animations should interfere, but I done deleted that code which had the problem, but I might can remake it for the sake of science and all.