Lightmass doesn’t necessarily scale up with the number of processors, each object gets rendered on a separate thread, so if every object has a thread on it, you can’t put more threads on the object to render it faster. What that can also mean is that you can finish all of the threads except for one if the object is large and complex and the other available threads can’t join in and help with the final object. That’s a limitation of Lightmass and hopefully something they can fix, because that’s a very dated limitation.