Hey @Mind-Brain ,
I can’t hide the truth anymore, I lied, it’s not about rabbits 
So here are some screens of my mess:
The casting is in the AI controller.
The Spawner is spawning a BluePrint driven by the AI controller.
The “New Var” in the AI controller is set to the spawner’s parent object class.
As you probably guessed, I’m pretty new to BluePrints.
I’m not sure I understand fully the concept of Casting …
I hope I gathered enough informations, tell me if you need more infos 