I’ve exposed a new project option which helps with the issue of the integrator adding energy. It’s basically a tradeoff between stacking stability and energy conservation so it’s up to the type of game you’re making.
https://github.com/EpicGames/UnrealEngine/commit/c8a733313af1aa39061afd92ea9ee3ca7662b790
This still doesn’t fix the problem where friction has little affect on the sphere. The problem here is that for a perfect sphere the contact patch is infinitely small. However, if you turn PCM on and use angular damping you should get reasonable results.
Hope this helps