Cube starts shaking when placed on a giant sphere

Hi all,

  I'm trying to place a cube of scale 1, 1, 1 on top of a sphere that is scaled 1000, 1000, 1000, however, I'm encountering a problem where it keeps shaking and slowly rotating/moving when it is on a surface of a sphere.

  I tried it with the Rigibody gravity and using a custom gravity script that makes sphere a center of gravity (as sphere represents the planet). In both cases, the cube starts shaking so I assume it is not related to my gravity script.

  The only explanation that makes sense at the moment is that the cube's flat surface is touching only a small point of sphere collider at each given time moment and that causes the shaking?

  Anyone knows how could I prevent that (preferably without using a custom script to lock and unlock GameObjects as that sounds more like a workaround than a solution)?

  Already tried changing almost all settings in the Project Settings > Physics tab. Also tried changing mass of cube, its drag, and angular drag - this can solve the issue, however, only when values are high enough to make cube almost impossible to move at all.

  Video demonstrating the issue: https://youtu.be/KWNiM5r3C_o - there are 2 copy-pasted cubes, one using Rigidbody gravity and another one using custom gravity script (P_Gravity).