Animation rigging doesnt work until I disable and re-enable Rig Builder

I'm making a shooter game and want to make my character hold weapons by changing the targets for hand TwoBoneIKConstraints throught script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.Animations.Rigging;
 using Bolt;

 public class WeaponManagerScript : MonoBehaviour
 {
     public GameObject[] slots;
     public Rig handRig;
     public TwoBoneIKConstraint rightHand;
     public TwoBoneIKConstraint leftHand;
 
     int held = 0;
 
     void Start()
     {
         //rightHand = handRig.transform.Find("RightHandConst").GetComponent<TwoBoneIKConstraint>();
         //leftHand = handRig.transform.Find("LeftHandConst").GetComponent<TwoBoneIKConstraint>();
         SwitchWeapon(0, 0);
     }
 
     void Update()
     {
         if (Input.GetKeyDown(KeyCode.Alpha1)) SwitchWeapon(held, 0);
         else if (Input.GetKeyDown(KeyCode.Alpha2)) SwitchWeapon(held, 1);
         else if (Input.GetKeyDown(KeyCode.Alpha3)) SwitchWeapon(held, 2);
         else if (Input.GetKeyDown(KeyCode.Alpha4)) SwitchWeapon(held, 3);
     }
 
     void SwitchWeapon(int current, int target)
     {
         held = target;
 
         Debug.Log("Switching from " + current + " to " + target);
         foreach(var obj in slots)
         {
             WeaponScript wep = obj.GetComponentInChildren<WeaponScript>();
             if(wep) wep.enabled = false;
         }
         WeaponScript awep = slots[target].GetComponentInChildren<WeaponScript>();
         if (awep) awep.enabled = true;
 
         Transform newRightHand = null;
         Transform newLeftHand = null;
 
         try
         {
             newRightHand = awep.transform.Find("RightGrip").transform;
         }
         catch
         {
 
         }
 
         try
         {
             newLeftHand = awep.transform.Find("LeftGrip").transform;
         }
         catch
         {
 
         }
 
         if (newRightHand != null)
         {
             rightHand.data.target = newRightHand;
             rightHand.weight = 1f;
         }
         else
         {
             Debug.Log("No right grip!");
             rightHand.weight = 0f;
         }
 
         if (newLeftHand != null)
         {
             leftHand.data.target = newLeftHand;
             leftHand.weight = 1f;
         }
         else
         {
             leftHand.weight = 0f;
         }
     }
 
 }

The problem is this doesn't work (target and weight doesn't get changed) unless I disable and re-enable RigBuilder compoenent in the editor when the game is already running (doing the same through script doesnt help). Can someone please help me fix this issue?