If you move a physics object before creating it’s impostor when it’s static, the physics object will move toward that direction at 0.01 world unit per hour. This must be because it has a tiny tiny tiny bit of linear velocity still imparted on the static object. Consider the reproduction here, look at the variables at the top.
BTW once you tell it to speed up yhe simulation, you’re computer might lag a bit. Look in your dev console to see the Y position of the ground printed out.
Also, I only started to notice that because I would be playing DND for 3 hours in Playtable and our figures would be sinking into the ground slowly over the course of our session. this is also posted here so others may find this bug and know what the workaround is.