physics - reproducibilty problems?

I have a level with an unstable initial setup of actors that should automatically start moving. Problem is, when the level is loaded they sometimes start moving, sometimes they don’t. Physically starting setup is close to the unstable equilibria, so the intial forces are quite small, but that’s the idea - changes have to be very slow at the beginning and they have to speed up with time. Making the objects larger and heavier patrtially solves the problem, but breaks other parts of the system

Any ways of making the physics more predictable?