I am only new here and don't have much expert advice, but i have experianced the same hting with my neons plenty of times, like 2 out of 4 of them would have big bellies, but it would dissappear in a few days, they acted fine and were eating, and i never noticed any eggs or fry!
So am eager to see everybody elses advice on this topic!
Well, whether they lay and produce offspring is one thing. But the large neons you see are females. I have harliquins, which are different, but there is a clear difference between males and females in them, and same with neons.
Wait till see what others say. Sorry, i aint never breed neons before>