How are you deciding they are not fertile versus dying due to bacterial infiltration?
What are you feeding the mating pair?
I know with my angels they danced and she released eggs for about 8 months before they became fertile even though they were big enough.
General wisdom was they needed better nutrition from being in a captive state. The male I got from my LFS where he hadn't eaten for at least a week. The owner gave him to me because he knows I keep lots of different foods around. I got the girl a few weeks later. I provide all the things an angel could want. Copepods, algae, sponges and frozen mysid which even though they are a 3 inch fish they spend all day picking at copepods, algae and sponges. So I was surprised that the eggs were infertile for 8 months because that is the best nutrition you can get.
I'm still not convinced the 8 months was nutrition but it's something to consider if you are trying to get fertile eggs.