Why model is falling apart?

When I import from the blender skeleton mesh and when in physics asset use physic simulation, model is falling apart.
What am I doing wrong? I am 3d noob.

Thanks

Your joints are missing. (Thats what connets the phys spheres together)

Im joining the mesh together(Ctrl+J). My bones are connected too. Bone attachment to the body using vertex groups. When I go to the physics assets and press simulation, object twitches and falling apart.

how it looks:

Maybe I’m wrong to do something in a blender.

Everything works when you do not change the default scale when exporting from blender (1).

How to make the right rig and more useful information here: