Loading Muiltiple Scenes Async

Hello, I have issues loading multiple scenes async. It is working, if I have only one Scene "background loaded". But if there are two or more "background scenes" because the script is attached to more than one object, the onMouseUp Method is only working for the first scene which was loaded async.

Thanks for your help!

 AsyncOperation async;
 
 void Start()
 {
 async = SceneManager.LoadSceneAsync(nextSceneNumber);
 async.allowSceneActivation = false;
 }
 
 OnMouseUp(){
 async.allowSceneActivation=true;
 }