Why are my crickets dying?

I've had a colony going for quite a while most are sub adult a few are adult (a couple thousand). Just recently they started dying on me. They seem to loosing control of their body and dying slowly. I usually see them on their back kicking there legs. I was using cricket gel and high quality dog food. So I cleaned a new cage made a $60 mix for the crickets and switched back to the old cricket gel I had been using. I thought it might have been the gel I was using because it smelled like bad eggs. After switching everything back more crickets are dying. The only thing I can think it could be is the fruit crates I'm using. But they are unused. Could there be something on them causing the crickets to die? Maybe some sort of insectiside? Or are these just left over crickets that are already infected?

What are you feeding them?

Someone lost a large colony of whatever insect they were rearing for research, and traced it to their organic lettuce testing positive for the residue of 17 different pesticides.

Whatever you're feeding them, I suggest rinsing it off thoroughly beforehand. Organic does not equal pesticide-free.

I am pretty sure it isn't the food. The babies that I am rearing are fine and healthy. The food that I am using is a recipe I found. It containers about 12 different ingredients. I just started feeding them that last night. I am leaning towards the fruit crates. My babies are on straight toilet paper rolls and they are fine. My adults are on fruit crates too and they are fine too which doesn't make much sense to me.