Why does this happen to my robot when using the script?

Unity Engine
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1 

using System.Collections.Generic;
using UnityEngine;

public class IKMB : MonoBehaviour
{
    public Transform goal;
    public ArticulationBody effector;
    public ArticulationBody baseBone;
    public float sqrDistError = 0.01f;
    [Range(0f, 1f)]
    public float weight = 1f;
    public int maxIterationCount = 10;

    private List<ArticulationBody> m_Bones;

    void OnEnable()
    {
        // Create a list of bones starting at the effector.
        m_Bones = new List<ArticulationBody>();
        ArticulationBody current = effector;

        // Add bones up the hierarchy until the base bone is reached.
        while (current != null && current != baseBone)
        {
            m_Bones.Add(current);
            current = current.transform.parent != null ? current.transform.parent.GetComponent<ArticulationBody>() : null;
        }

        if (current != baseBone)
            throw new UnityException("Base Bone is not an ancestor of Effector. IK will fail.");

        // Ensure the base bone is included in the list
        m_Bones.Add(baseBone);
    }

    void LateUpdate()
    {
        Solve();
    }

    void Solve()
    {
        Vector3 goalPosition = goal.position;
        Vector3 effectorPosition = m_Bones[0].transform.position;

        Vector3 targetPosition = Vector3.Lerp(effectorPosition, goalPosition, weight);
        float sqrDistance;

        int iterationCount = 0;
        do
        {
            for (int i = 0; i < m_Bones.Count; i++)
            {
                RotateBone(m_Bones[0], m_Bones[i], targetPosition);

                sqrDistance = (m_Bones[0].transform.position - targetPosition).sqrMagnitude;

                if (sqrDistance <= sqrDistError)
                    return;
            }

            sqrDistance = (m_Bones[0].transform.position - targetPosition).sqrMagnitude;
            iterationCount++;
        }
        while (sqrDistance > sqrDistError && iterationCount <= maxIterationCount);
    }

    public static void RotateBone(ArticulationBody effector, ArticulationBody bone, Vector3 goalPosition)
    {
        Vector3 effectorPosition = effector.transform.position;
        Vector3 bonePosition = bone.transform.position;

        Vector3 boneToEffector = effectorPosition - bonePosition;
        Vector3 boneToGoal = goalPosition - bonePosition;

        if (boneToEffector == Vector3.zero || boneToGoal == Vector3.zero)
            return; // Prevent invalid rotation calculations

        Quaternion fromToRotation = Quaternion.FromToRotation(boneToEffector, boneToGoal);

        // Convert the rotation to local space
        Quaternion localRotation = Quaternion.Inverse(bone.transform.rotation) * fromToRotation * bone.transform.rotation;

        // Apply the local rotation to the articulation body's drive target
        ArticulationDrive drive = bone.xDrive;
        drive.target += localRotation.eulerAngles.x;
        bone.xDrive = drive;

        drive = bone.yDrive;
        drive.target += localRotation.eulerAngles.y;
        bone.yDrive = drive;

        drive = bone.zDrive;
        drive.target += localRotation.eulerAngles.z;
        bone.zDrive = drive;
    }
}