How frustrating, good breeding behavior, fertile eggs, hen setting normally and then all of a sudden she abandons her eggs. When this happens, it is likely an overdose of vitamin E and the hen rather than completely her cycle has been overstimulated to start the process all over again. In some cases she makes it to hatching the chicks but then won't feed them and instead wants to re-nest again.
Vitamin E in the right amount produces fantastic results but since it is fat soluble it is stored in body fat, overdoses produce disastrous results.
Also be sure to provide a dish of hemp seed while she sets. This helps keep her happy sitting and provides necessary manganese. The calcium/manganese ratio regulates the rate of hatching, imbalances of these minerals may cause early or late hatching.
When everything is clinking exactly right my hens hatch on the 13th day, otherwise the 14th day.