[linMcHlp]

I am guessing, that they “hit a snag” ran afoul of something . . . somewhere between 8,500 and 9,500 ft. That puts the submersible in the 1.75 hours, time zone of descent.

If they have a redundant atmosphere scrubber system (mentioned in 1 report), then that redundant scrubber system might use a separate, emergency backup power source.

Yet, “the snag” might be “simply” the very cold water.

North Atlantic, at depths over 4,000, the seawater may be around 32 - 38 deg. F (0 - 3.6 deg. C).

[New Perspective]

Pressure was the issue and this was the result.

Very quick video of what happens.

Compression