Temperature change could be a reason but I can assure you that wasn't the case with mine. Their water temperature only changed +/-1 degree.
I think mine perished as a result of poor/low oxygenation. The ones in the main tank were fine until I had to turn off the filter because it was starting to suck up a few eggs. The tank that had no air stone was the first to fungus over.
Given the habitat and the fanning behaviour of the females, i´d agree that dissolved oxygen is likely to be a crucial factor for egg development. Best of lucks to everybody whose giving Pachytriton a go!
I left half the eggs in with the female then split the remaining half in between two containers. One container was just a pond setup with tons of plants and the other setup was a simple, plain tank with just an air stone.
I had another female in a different tank lay as well but she ate all of her eggs shortly after I saw them.
I do have a theory on what may have gone wrong. Needless to say, I'm looking forward to being able to test it out next year.