Unstable Rigidbody with freeze position


I create a tower using several boxes (rigidbody + box collider). When I select Rigidbody->Freeze position (x or z) then the tower becomes unstable. Boxes start to slide very slowly and whole tower collapses.
When I use no constraints on rigidbody then the tower is stable.
I’ve tried everything in physics settings, collision detection, interpolate, etc. Nothing so far.
Here is a sample project to illustrate my problem: Dropbox - File Deleted - Simplify your life
I’m using Unity 2018.2.11f1

No answers so far :frowning: There is also a similar question, asked in 2016, still not answered, so I think it might be a bigger issue that no one knows how to fix.

For now I ditched position constraints. Instead I created small script that works like a spring joint in one axis:

void FixedUpdate()
   float force = 1000;
   float damping = 10;
   rigidbody.AddForce(new Vector3(0, 0, (originalPosition.z - transform.position.z) * force - rigidbody.velocity.z * damping));

So far it works for me. Stacked boxes are stable and they are sort of locked in one axis.