The only thing I know that would cause this would be probs with temps, but you're other clutches appear healthy so idk. I'm sorry for your losses but glad that at least two of the lil worms seem to have made it! Wishing the best for you and will be interested to know how your other clutches fair... God forbid, but if they appear to have issues it may have been a power surge, the kind that shuts everything in the house of momentarily but not long enough to reset clocks? I hope that isn't the case n that this was some fluke incident!