i just had the same thing happen and im wondering now if it had anything to do with the holes being plugged....i did this for the last 3 days on the last hatch and it was fine....i thought it was one hole plugged one hole unplugged 1-18 and both 19-21? i had 6 eggs....today was day 24 and i just cracked them all open and all were fully formed and dead....i cant figure out whats going on....but maybe that was it...lack of oxygen? i find that strange tho if they hadnt even pipped through the air cell?