Friction simply doesn’t work. It doesn’t matter if one sets it to 1 or 50, objects keep sliding and never fo to sleep at all. The only result of setting a very high friction value is an evident FPS drop, but the objects keep sliding on each other (i.e. coins on coin pusher, coins never stick on the surface nor on one another as expected).
Unity Physics doesn’t use sleeping.
Also, with low iteration count in the solver (see the Physics Step authoring component) friction is only approximate.
To mitigate that, enable the “Contact Solver Stabilization Heuristic” in the Physics Step authoring component which will improve stability of rigid bodies for stacking cases.