On occasion, I think it can be normal to lose a bird aopround a year old or even when they first start laying. I don’t have statistics, but I have lost a couple that just seemed healthy and later found them dead. I think heart problems are usually the cause. Later, I have started doing necropsies on older birds, just to look at the organs to see if the liver, heart, intestines, crop and gizzards were normal looking. Looking at some necropsy photos here can help later on if you do any. Sorry for your loss, and if possible , if you lose others get a professional necropsy by your state vet if the death seems unexplained.