According to documentation USceneComponent doesn’t have it’s own Tick() neither it overrides it, it’s inherited from UActorComponent which does have a tick component.
Perhaps Tick() call from component causes an additional Tick() on Root, as it’s higher in hierarchy, but that would only execute RootBodyInstance->AddCustomPhysics(OnCalculateCustomPhysics); second time.
0lento, do you mind if I post your code in the Bug Reports? Maybe someone from Epic can take a look at it.
But I can call PhysicsTick() instead of normal Tick() just fine, even with sub-stepping enabled, setting location of objects and AddForce() works and as expected it crashes on DrawDebugLine(), so at least I know it’s being called with proper frequency.