Why is the mouse cursor blocked when using FPCController in Unity?

Question

Unity

I have a problem.
There are two scenes in Unity.
One is the menu. The second is the level.
The first one has a Start button.
The second one has an FPSController object (with a First Person Controller script) and a script:

void Update()
    {
        if(Input.GetKey(KeyCode.Escape)){
        	SceneManager.LoadScene("Menu");
        };
    }

I start the game, press "start" and the scene is loaded - the level.
I want to go back to the menu, I press Esc, I exit, but when I click on "start" again, the mouse disappears and locks, I press Esc, it unlocks and appears, but the scene with the level does not load.