Rigidbody not sleeping

The docs say:

“If you have a sleeping rigidbody and you move a static collider (A collider without a Rigidbody attached) into the rigidbody or pull it from underneath the rigidbody, the sleeping rigidbody will not awake”

I tested this with two cubes. One with a rigidbody and the other with just a box collider. After leaving the rigidbody for a while after it landed on the box collider cube, I presumed it would be asleep and removed the cube from underneath. But the rigid body just continued to fall. I have played around with the physics settings but still nothing has changed the outcome.

Is this a bug?

No. It isn’t a bug since it’s not so much a feature, as a warning.

It’s telling you about odd cases where the physics system may not work perfectly, and you may have to help it with code (or just not do what you were doing.) There’s generally no guarantee just when or if an object will sleep. If you really want to test, you can give it a sleep command. But sleeping is really a behind-the-scenes time-saver for the system.

In your case, you could check off use-gravity, set kinematic to true, or maybe lock the Y-axis.