i have seen round plumb ones that are infertile and also fertile ones that have gone mouldy,you do`nt even have to touch or pick hem up to candle them.
once you have had a few sucesses and failures you know what to look for and how to deal with what happens.
I woulf go back to basics,eggs in lidded containers with pre moistened vermiculite etc half burried in medium and covered with a moist paper towel,check weekly.if towel is dry remoisten,if not do nothing and so on till end of incubation.To be honest i have never used a humidity gauge for any of my reptile hatchihgs till this year.Birds are different kettle of fish.