Hi,
a prefab can not reference a scene object, so in your third screenshot, that's why the gameobject ref disappeared, a prefab can only reference itself and its children, that's all, when instantiated, you will have to reference gameobjects one way or the other from outside, or using findGameObject.
- I don't think you need to use Findclosest here, you are not interested in distance between gameobject, but only to get the audiolistener, so simply use FindGameObject with a tag "audiolistener" and add this tag to your audiolistener, then it will work.
Bye,
Jean