Custom serializable class not serialized

Hello,

I've a custom List<> (just adding events to the lists methods) implementation and a SerializableDictionary in my project. Both of them are set up to be serializeble. The generic type of the list is another MonoBehaviour and the dictionary contais another MonoBehaviour as the key and simple custom class (which is serializable as well) as the value. The Monobhevaiours are set up to be executed in editor mode.

Now when i close the Editor or start the game the both the custom List as well as the dictionary are set to null. I don't know why this happens as I've checked that everyhing is serializable.