There are lots of reasons for gular edema. I haven't found Vitamin A to cause a problem but I suspect synthetic D is a problem. I think the cricket farms feed something to their crickets that builds up in the crickets' bodies that causes a problem with some species. I've found certain cricket shipments will cause edema in my collection of quads and graciliors and it will be immediate.
Major organ failure will cause edema. Also, a protein deficient animal will develop edema. A specific protein is needed to keep the blood fluids inside the blood vessels, so if an animal is protein deficient, lymph fluid will leak out of the blood vessels into the spaces between the cells (edema). Liver and kidneys are involved in protein metabolism.
It's a complex problem.