Vivid imagery befitting the general reliability of Bluetooth (witness me covering one of my EarPods to get the other one to connect up and sync with my phone at least once a day) but putting all the pieces together, my best guess is that the pressure vessel split at one of the seams between the cylindrical carbon fiber center section due to fatigue at the joint, well above their target depth. There's a reason why every other DSV designed to reach those depths uses a single-piece spherical pressure vessel.