There are chemical CO2 scrubbers that don't need electricity, so in principle you can die from lack of O2 while having livable CO2 levels. (though now you mention it I feel that the sub that failed it's depth rating test due to hull fatigue and then posted an FAQ about how it didn't need a rating because "disruption" does not have emergency CO2 scrubbers)
There are chemical CO2 scrubbers that don't need electricity, so in principle you can die from lack of O2 while having livable CO2 levels. (though now you mention it I feel that the sub that failed it's depth rating test due to hull fatigue and then posted an FAQ about how it didn't need a rating because "disruption" does not have emergency CO2 scrubbers)