I was watching a youtuber by the name "Vintage Beef" and he experience an issue where a chicken had wandered into a cave and was laying eggs and zombies would spawn. These zombies would pick up the eggs and this process led to lots of zombies that would not de-spawn. Only thing I would recommend is to remove eggs from the items zombies can pick up. This issue isn't too likely to happen but I thought it should get some attention.