Good to see the new update. I've make some tests with modifications. Test craf from ObsessedWithKSP.
After more deeper source investigations and unity docs smoking i've found one of mistake, we cannot just substract or sum anchor and connectedAnchor vectors, bc they are in different spaces local spaces, anchor is a joint.RiggidBody local and connectedAnchor is a joint.connectetBody space. The thing i don't understand is why rotating models have sometimes has different behavior on anchor positionint than translating models. Maybe its its models problem, but i dont have models sources, so cant test it, or it's ksp scene import behavior.