These are the Shimano Pro Missile bars but the older version. The "failure" was at the junction between the stem and the bar. I had carbon paste between the bar and the stem with the proper torque on the stem bolts. I was in the bull horns standing at max power and the joint released such that the bar rotated instantaneously and it felt like I dropped my body weight on the arm that was transferred into my shoulder.
I had used the setup before. Maybe the stem bolts needed more torque?