I don't think we've talked about the controls of this submarine enough. Only 3 vessels in the entire world can transport people down to these depths and these guys decided to do it with a system piloted by a BLUETOOTHED madcatz gamecube controller.
I reject literally all of your "most likely" scenarios. The most likely scenario to me is the bluetooth dongle went out. The batteries in the wireless controller went out. The knock off radio shack xbox controller got stick drift. The controller banged against the hull during the rockey launch and broke halfway down.
Literally everything else about the vessel can be in working order, but if that little tiny fragile bluetooth connection between the controller and the sub breaks then they're dead in the water. They have zero redundancies for this aspect of their design.
