singleton becomes null?

Hi, I am new to unity, I have a singleton class whose instance keeps changing to null whenever I pause/resume the app. Any idea why?

Here are the details:

I created a class derived from MonoBehavior, and set a singleton instance of it as the object Awake()s like so:

 public class MyClass : MonoBheavior {
     private static MyClass _instance = null;
     public static MyClass instance { get { return _instance; } }
     public void Awake() {
         _instance = gameObject;
         DontDestroyOnLoad(gameObject);
     }
 }

The script is attached to some stub prefab object on the scene so it gets run as soon as the scene starts. I see the Awake method getting called ONCE when the scene starts, but if I switch to some other app and return to Unity, I see the app-pause/resume event being fired, and after that, the MyClass.instance is null, and never gets back to being non-null..

What am I doing wrong? tnx