An animation's sub instances will tick twice per frame if a post processing BP is set.
Place the mannequin in the level using an Animation BP with a sub instance.
Call a function on the sub instance's Update Animation event.
Set a post processing BP on the mannequin's skeletal mesh.
Notice how the sub instance's update event is called twice per frame
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-80527 in the post.