Your standard shipping container may come with two or four vents. These vents, positioned near the roof, are often damaged due to mishandling of the container. When the humidity is high, the container gets moist from the evaporation and gets condensed. Once the condensation collects enough it will drop the collected moist in water droplets to the plywood, leaving it there to soak. Thus, the plywood gets waterlogged and will eventually rot.  Simple cycle of warm evaporated water rising, collecting, then coming back down.