sounds like something got in there and is thriving. Remove everything and clean your bin with a 10% bleach solution, rinse it well and let it air out to make sure that there is no residule odor of bleach. either replace the egg flats or pop them in the microwave for a bit to fry the little buggers and their eggs that may remain. ensure that there are none with your roaches when you replace them and you may have the problem licked. at least that is what I would try first. also make sure that the cover for your roaches is secure at all times including the ventilation screen. this should make sure that most unwanted pests stay out