I lost my very first clutch last year to this same issue. My water to vermiculite mixture was almost perfect just a little too wet and it made all the eggs rot IN the future all of my eggs will be incubated on a grate so theres no risks. Also if any sort of bacteria or chemicals somehow get on the substrate the risks are even higher. Lastly if your bator is set up well you shouldnt have to worry about this but sometimes you can have hotspots in your sbstrate and unless you lift the eggs and visually inspect the bottom you can not tell they are being burned. They bottom will begin to become brown and by that time its too late.....