I’ve had the same issue. I get my air filled up by breaking and collecting water and moving into the gaps of air before they refill with water. My oxygen meter refills when i do this, but after some time doing this i will start to drown, regardless of having a near full O2 meter
I was trying to reproduce this, but kept crashing before I could recreate the problem. In any case, I’ve added these comments (and the crash I was experiencing) to the bug database, so with any luck, if the crash is fixed, then hopefully this issue will be fixed along the way as a consequence.