The constituents in public water sources can vary from day to day. Distilled water is pretty cheap, considering how time and labor intensive lith can be. Many possible sources of frustration, yes.
If you spend any time developing face down in the tray . . .the path to infectious develepment is cumulative, so if a print is left face down for ten or fifteen seconds early in development, it is no different than leaving it face down during the infectious stage. Is the floor of your lith tray dimpled perhaps?