Seems like no one is talking about the toll the compression and decompression cycles had on the hull integrity. The sub took a few trips so there was probably a weak point which developed in the hull. ...could have even been some amount of ultraviolet ray and salt water weakening of the hull materials while sub was topside or in the water. Needed more white 50 year old engineers, corrosion experts and deep dive masters. Still a sad way to go....however quick.
I have no idea.
According to what else Ive read it has taken about 50 trips and the body is swapped replaced about every two.
Unlike the metal alloys used by the navy the fibers in the carbon body cannot repeatedly flex. The damage to the material when it is stressed causes fibers to start to break and cannot effectively be seen or tested for until its too late.