2d physics problem


In one scene I created a new balance with the physical. New on the scene the balance works well.
When the amount with the size prefab on the scene of the game to test it is not working. Has anyone had the same problem?
Any solution?

The image below icon corresponds to the scene in the game where the balance is blocked and chest crosses the plane without collision.

The image below portrays the scene where I created a new balance and everything works fine.
The scene of the game affects the physical? I do not understand the probema! :frowning:
Help !!!

Now I have addressed these issues. In the two platforms I have added 2 more boxcollider2d, now holding the box but after several seconds the box slowly, slowly, slips falling from the platform. I enclose picture:

I also set the mass rigidbody the box (0.1) to make it lighter.
Does anyone know this problem?