Zombies and wolves seem to have a hard time following people into cargo containers. Due to the abundance of them on the modded map Namalsk this has become more of a problem.
It seems to happen more when the zombies approach the container from the sides.
I think the zombies can not navigate doors that are swung open. This is probably an issue with all doors in DayZ but most visible with cargo containers because of how the AI encounters them. They approach on the side and get caught on to them. I've seen it with the barracks building too.
Perhaps there is a difference if they are giving active chase and the door state changes vs they decide to chase and doors are already opened.