my bow string moves so wired with ControlRig

i use a Control Rig to Draw my bow string, which looks like this

and in ABP_Bow, draw state looks like:

i pass arrow socket which is in the right hand’s bone to the bow

then in the bow’s class, i pass it to the ABP class of the bow

and here is the initial transform logic

sadly in the result, the string turns out going into mad

any help, thanks very much.