To reproduce:
1. Create a new project.
2. Create "Cube" in Hierarchy.
3. Add Cloth component to the Cube.
4. And set Cloth's "Sleep Threshold" to 4.8
5. Play scene for a couple of times. Sometimes cube will fall all the way down, other times, it will quickly stop (sleep)

Actual result: Object sometimes drops down, sometimes stops.
Expected result: It would always have a consistent result.

Reproducible: 5.4.4p4, 5.5.3f1, 5.6.0f3, 2017.1.0a6