The AudioStreamPlayer node needs to be separate from the scene, so the scene tab needs to look like this.
New Scene
> The game scene
> AudioStreamPlayer
and instead of using get_tree().reload_current_scene()
, load the scene and instance it like this.
export var level : PackedScene
var levelInstance = load(level.get_path())
func _restart():
your_current_level_var.queue_free()
get_owner().add_child(levelInstance.instance())