Film director James Cameron has expertise in designing and testing these submersibles, and he has many criticisms of the design of the sub that imploded, and of the hubris of the CEO who ignored repeated safety warnings from the diving community. He also mentions that the sub seems to have been attempting to resurface when it imploded, suggesting that they were aware the hull was starting to fail.
Cameron made a documentary about his sub called “Deep Sea Challenge” that’s pretty enjoyable. It’s available for free on Pluto TV, for those able to VPN into the USA.
Cameron’s sub wasn’t officially certified, but it was extremely well tested and he’s been clear that he never would have let anyone else use it without certifying it first.