Actors falling together or flying away with usage of multiple joints

We try to build up an excavator arm in physics. For that we have to use mutliple joints and actors workind together. The usage of a few number of actors and joints (two or three) working well, but if we use more of them the model becomes more instabil and the actors fall together or fly away. Sometimes I found a stable configuration but if I edit the parameters only a little bit like I adjust a linear limit from 0.3 to 0.4 the model beocmes instabil.
I’ve tried revolute and prismatic joints as well as D6Joints.
We think that could be a problem of cycle times of our program.

Is that possible? How can we proof that? Perhaps something else goes wrong. Do you have an idea?

We use PhysX 3.3