restart a game in unity

Question

The game restarts after completion, but upon restarting, it unexpectedly exits after a few seconds. What steps should I take to debug this issue? Is there a need to change in the Unity editor?

I want this game in Unity to restart with a delay of 4 seconds after its completion properly.

using UnityEngine;
using UnityEngine.SceneManagement;
using System.Collections;
using TMPro;

public class BallController : MonoBehaviour
{
    private float collisionTime = 0f;
    private bool timerActive = true;
    public float collisionThreshold = 5f;
    public float restartDelay = 4f;
    public TextMeshProUGUI timerText;
    public GameObject cylinderPrefab;

    private GameObject cylinderObject;

    void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.CompareTag("CylinderTag"))
        {
            collisionTime = Time.time;
            timerActive = true;
            cylinderObject = collision.gameObject;
        }
        else if (collision.gameObject.CompareTag("Ground"))
        {
            timerActive = false;
            UpdateTimerText();
        }
    }

    void Update()
    {
        if (timerActive && Time.time - collisionTime > collisionThreshold)
        {
            if (cylinderObject != null)
            {
                Destroy(cylinderObject);
            }
            StartCoroutine(RestartGameAfterDelay(restartDelay));
        }

        UpdateTimerText();
    }

    IEnumerator RestartGameAfterDelay(float delay)
    {
        yield return new WaitForSeconds(delay);
        SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);
    }

    void UpdateTimerText()
    {
        if (timerText != null)
        {
            float remainingTime = Mathf.Max(0f, collisionThreshold - (Time.time - collisionTime));

            if (timerActive)
            {
                timerText.text = $"Time: {remainingTime:F1}s";
            }
            else
            {
                timerText.text = "";
            }
        }
    }
}