When I press the play button once the game loads, but when I press it a second time the game is static

Hello, I’m a beginner in unity and I’m having an issue with the main menu.

So I check multiple videos on how to make a main menu and it worked tho, when I press the play button once, the game loads and I’m able to play the game but when i go back to the main menu and press the play button again, the game is static and I’m unable to move the character not the water is moving.

Don’t know if it’s an error with the code or something else is missing

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class MainMenu : MonoBehaviour
{

    public void PlayGame()
    {
        SceneManager.LoadSceneAsync(SceneManager.GetActiveScene().buildIndex + 1);
    }

    public void QuitGame()
    {
        Application.Quit();
    }

}

are you unloading the game scene when you return to the menu again?