
Originally Posted by
martinsustek
I am not sure about the real reason. But the fact is, that there is massive rigidbody with many individual colliders, and most of them are laying on another grounded (kinematic) rigidbody with many individual colliders. In Unity 5.4 the top rigidbody goes to sleep, but in Unity 2018 it does not. Probably there are some jittering forces that wakes it up all the time, so engine must calculate millions of collisions each frame instead of keeping the things sleeping.