Unity physic, buildings of the blocks are destroyed by themselves

Why? How can I fix it?

 

Try playing with the physics options (Edit > Project Settings > Physics), especially:

• Default Solver Iterations: increase
• Default Solver Velocity Iterations: increase
• Enable Adaptive Force
• Contacts Generation: try Persistent Contact Manifold
• Friction Type: Two Directional Friction Type

Also ensure the physics materials assigned to your boxes are properly configured for low bouncing.

 

I've had this problem before too, I think bumping up the sleep threshold a bit might help.(except for the instantiation moment)