I can second the "death by orange stuff." Oh my gosh! It's shocking! I don't know about the Nature Zone, only because I don't use it. I use the dry powdered grain based food and mix in some of the vitamin powder and calcium powder I dust the crickets with. They seem to thrive. I also had the keeper and just felt like it didn't have enough space when I went above the 50 cricket mark. Not enough ventilation, and it was impossible to clean out the poop. I found that buying a cheap aquarium with a wire clamp down top worked better. It let me take the top off and clean it well.
I use a soft bristled paint brush to gently "sweep" the bottom of my cage. The healthy crickets flee the "Brush of Doom" and the moltings, poo and dead crickets/unhealthy crickets get piled up. Then I use the crevice tool of my vacuum to suck up the pile.. I stack egg cartons to give them lots of space to hide and keep them from climbing each other, which is very unhealthy for them, and saves me "floor space" for their food and water saucers. Then, when I get a new batch in, which I try to time when I'm almost all out, I Clorox wipe out the aquarium and then wipe with water and let air dry.
It seems like a lot of work, but I have VERY healthy crickets. I have very little die off comparative to before I started doing all that. A lot of what affects cricket life span comes down to husbandry. You have to keep them like they're pets. They need dry, warm and lots of room.
That said.... It COULD be a virus. Every once in awhile a weirdo virus sweeps thru cricket-town. It's good for killing the buggies off in batches. Typically it is NOT dangerous to your beardie. It just does the buggies in.
Have you tried contacting where you ordered them from? Maybe try Googling them and the word "reviews" to see if there are other issues people have reported. Also try looking around on here.