Sand in a nutshell. fine sand or deep sand layers—can cause hypoxia or anoxia (no oxygen) in substrates by restricting gas exchange and water flow. While sand is often thought of as airy, in aquatic or heavily saturated environments, its small particle size can compact and seal off lower layers, preventing oxygen from penetrating. Plastic pots, don't help but sand will just destroy oxy.
As microorganisms progress through flower they scavenge more oxygen in competition with the plant. As micros slowly add more and more co2 into medium this slowly increases moisture retention of medium, once moisture in the medium goes above a setpoint, oxygen movement speed swings from 10,000 times slower than air in soil to 320,000 times slower in saturated soil.
Soon as that happens its all lactic acid and 10% of the energetic output, irrespective of any other metric. Everything begins to fail.