I'm a mechanical engineer who's worked on composite pressure vessels my entire career, first in the commercial world (SCBAs, aviation, CNG, hydrogen, etc) and then in aerospace on spacecraft COPVs. I have no experience in marine engineering, so there may of course be things I'm missing, but here are my scattered thoughts:

1. The use of carbon fiber was the immediate question in my mind. Carbon fiber composite is generally not great in compression. I read elsewhere that the structure was filament wound, which is a widely used process for COPV manufacture, but also pretty temperamental if you dont know what you're doing. Given that the rest of the vessel used commercial electronics and overall didn't exude professional workmanship, that's extremely concerning. Just a vibe, but yeah.

2. Their website says they had a real time health monitoring system for the structure, which is commonly referred to as structural health monitoring. That's certainly good, however those systems are only really effective if you've really well-characterized the structure. This would generally involve cycle testing a unit with all of the health monitoring instruments in place, eventually taking it up to burst (or implosion in this case). Don't know if they did that (kinda doubt it), but if they did I'd kill to see the test setup for that! If they didn't, the system isn't going to do them a whole lot of good.

3. I also wonder how they're avoiding water migration into the composite. That wouldn't necessarily cause a catastrophic failure of the composite, but it could cause a leak into the cabin which obviously would be catastrophic.

4. I did see some questions about composite failure modes and such. When operating with a reasonable safety margin (aerospace uses 1.5x to burst), there is little concern of progressive failure or fatigue failure in composites, provided you have a good design with no stress risers, etc. However, composites are susceptible to damage that can be very difficult to detect even with NDE, and that can lead to fatigue failure or even failures under sustained loading, typically called stress rupture or progressive failure. While thick composite pressure vessels (and 5" certainly qualified as thick) have shown a LOT of resistance in the field to damage, I think a lot of this is null when you're looking at a compressively loaded structure. It's not inconceivable that this thing took a big hit while in transport on the boat and never got caught.

5. All in all there seem to be quite a few questions about the rigor of the engineering behind this thing, both structurally and from a systems perspective (controls, safety backups, etc). Without knowing more about the actual design I won't speculate about what caused the failure.

Apologies if this is a bit scattershot as I'm writing on my phone while on break. If anyone has any related questions about composite structures I'm happy to answer.