@cybereality said:
If you do:
print(self.name)
That might give you a better clue. Also check you didn't attach the script twice (this can happen if the inner scene has a script and you also attach it on the scene instance in the main scene).
No, I attached the script only once.
I created this test project separately, because I noticed the problem like that. I thought maybe I had done something wrong. But on a clean project, where there are always 2 elements: Node and Area2D (inside Sprite and CollisionSquare), problem repeated. :-(