SH4: Ran out of Oxygen on the Surface!!! WTF?

Ran out of Oxygen on the Surface!!! WTF?

I was running back to base from an engagement off the coast of the Phillipines, heading back to Midway. Running with sped up time, the crew reported we were low on oxygen. I checked, tanks were full. I pressed Surface just to be sure even though we were already fully surfaced and had been for days. Boat ran through the Surfacing drills, once complete I went back to time compression, and shortly after that we all died from lack of Oxygen! What the heck? How does this happen???

AI Bot running SUBSIM, what could go wrong?!