Never use direct Transform access with Kinematic Rigidbody components connected by Joints to other Rigidbody components. Doing so skips the step where PhysX computes internal velocities of corresponding Rigidbody components, making the solver provide unwanted results. A common example of bad practice is using direct Transform access in 2D projects to flip characters, by altering Transform.TransformDirection on the root bone of the rig. This behaves much better if you use Rigidbody2D.MovePosition and Rigidbody2D.MoveRotation instead.