Just the attack skill, only used constants mod and what it has to offer and the error code points to damage effect scales calculation, doesn't really say where or what group is.
Honestly could be something simple like loading problem with custom images that maybe bit too large size for what its use for, just creating stress on game engine having to resize image and use said image in attack animation causing it to stagger when force to speed up which can end up skipping something leading back to problem. Give that wild theory try later.