EventSystem.current.currentSelectedGameObject.name NullReferenceException

In my MenueScene I have a few Buttons in a Scroll Rect in a Canvas and when i transition from one Menue to the other one I deactivate (Interactible == false) all Buttons in the Scene until the transition is finished. Then I activate the Buttons on Screen with the .setOnComplete from the LeanTween PlugIn.
Sometimes, not always, if i click a Button exactly after the Animation is finished this error is showing up:
NullReferenceException: Object reference not set to an instance of an object
and it points to the onClick method where im trying to get the name of the Button that is pressed with EventSystem.current.currentSelectedGameObject.name.

//Animation

Code (CSharp):

1.  
2. public static void slideAnimation(int direction, GameObject alt, GameObject neu, bool destroy) {
3.         foreach (GameObject o in GameObject.FindGameObjectsWithTag("zoom")) {
4.             if (o.GetComponent<Button>() != null) o.GetComponent<Button>().interactable = false;
5.         }
6.         if (neu != null) {
7.             neu.name = neu.name.Replace("(Clone)", "");
8.             neu.transform.SetParent(GameObject.FindGameObjectWithTag("canvas").transform);
9.             neu.transform.localScale = new Vector3(1, 1, 1);
10.             neu.transform.localPosition = new Vector3(-direction * GameObject.FindGameObjectWithTag("canvas").GetComponent<RectTransform>().rect.width, 0, 0);
11.             LeanTween.moveLocalX(neu, 0, 0.5f).setEase(startAnimation.bouncycurve).setOnComplete(() => {
12.                 foreach (GameObject o in GameObject.FindGameObjectsWithTag("zoom")) {
13.                     if (o.GetComponent<Button>() != null) o.GetComponent<Button>().interactable = true;
14.                 }
15.             });
16.         }
17.         if(alt != null) LeanTween.moveLocalX(alt, direction * GameObject.FindGameObjectWithTag("canvas").GetComponent<RectTransform>().rect.width, 0.5f).setEase(startAnimation.bouncycurve).setDestroyOnComplete(destroy);
18.     }
19.  

//onClick

Code (CSharp):

1.  
2. public void onUpperCategory() {
3.         string helper = EventSystem.current.currentSelectedGameObject.name;
4.         GameObject alt = GameObject.FindGameObjectWithTag("slide");
5.         GameObject neu = Instantiate(Resources.Load("Prefabs/Categories/Ca" + helper, typeof(GameObject)), Vector3.zero, Quaternion.identity) as GameObject;
6.         sV.slideAnimation(-1, alt, neu, true);
7.     }
8.  

Yes i have ONE EventSystem in my Scene at all times

If someone could help my I would be very thankfull, Cheers Ricca

 

Necroed. "EventSystem.current.currentSelectedGameObject" is generally null when UI elements are not in focus.