You guys talk about tightening, but are you using a torque wrench? Very important daniel son. Disregard if you already know.
Think of each stud like a rubber band. If they aren't all pulling at their full potential, one or two are taking more load than others. Taking more load leads to the steel stretching past its elastic limit. Once the steel gets stretched, it doesn't pull any more resulting in a loose stud.
A loose stud now wiggles and screws up the the hole in the knuckle, in addition the load gets transfered from the loose stud to another stud causing it to yeild. The same thing happens when a stud is over-tightened.
So essentially the optimal condition is where all 4 studs are stretched, or pulling equally right up to their max limit. If a stud has been stretched too far, it never regains its original elastisity. :;