How can i fix weird physics bug/glitch ?

i have stange bug with physics , when unfreezing parented rigidbodies . i have made a video .

my code for chopping down trees and unfreezing rigidbodies :

 using UnityEngine;
 using System.Collections;
 
 public class CHOPCHOP : MonoBehaviour {
     public Rigidbody body;
     public Rigidbody[] crystals;
     // Use this for initialization
     void Start() {
         foreach(Rigidbody crystal in crystals) {
             crystal.constraints = RigidbodyConstraints.FreezeAll;
         }
     }
     
     // Update is called once per frame
     void FixedUpdate() {
         if (Input.GetKey(KeyCode.T)) {
             body.AddForce(Vector3.forward * 5);
             foreach(Rigidbody crystal in crystals) {
                 crystal.constraints = RigidbodyConstraints.None;
             }
         }
 
     }
 }