Skeletal 2D Animation does not work

I started working with unity 2d skeletal animations and I imported a psb file to unity. But once I created all bones and hit “Apply” some of the sprites went in a weird position, and some sprite stopped rendering. When I dragged the GameObject into the scene, I saw that a part of the sprites lost their sprite renderer. If I dragged the bones in the scene, a couple of them seems to be still working, but most of them stopped working.

I suggest you follow this tutorial for a better understanding: