When you switch level entire world is cleared and all actors assign to it are automatically deleted and all data in them is lost, only pure UObjects that are not assign to world will be still alive. UE4 has designated class to store game-wide varables and code called UGameInstance
Can’t find documentation that use blueprint but here is video tutorial using it in blueprint:
https://docs.unrealengine.com/latest/INT/Videos/PLZlv_N0_O1gYqSlbGQVKsRg6fpxWndZqZ/78XJYBfWXAA/