I agree with the rest, toxicity issue in all likelihood. I keep my crickets in the rubbermaid containers too. Wash all veggies and fruits you feed them, wash the container with hot water only. Cut a large square out of the top of the container and silicon a mesh or screen top on. Keep them in a dark place where they get some air flow and keep them clean and dry at around 75-80 degrees. Look in on them once a day and look for dead ones. Those dead ones might have had parasites, poisoning, or simply bad genes, regardless, remove them before they get squishy and stinky as they will affect the rest of the crickets and more will die. Particularly if the rest of the tiny brained little omnivores try to cannibalize the dead ones. When you clean the water and food dishes use only hot water. I use a cut up sponge for the water dish to keep them from drowning. I also use a lot of fruits like apple and orange. I also use quaker oatmeal as a dry feed and mix a light dusting of vitamin supplements in. Thus far, I have only had a handful die out of the 1000 I ordered from Armstrong almost two weeks ago.
I do the same with mealworms, soon to be replaced with superworms, and they are on the way to metamorphosing into beetles. My Chameleon loves the pupae and recently shed grubs.