Humidity "fog" is a common problem with all dichromated colloid emulsions.
Gravure resist is another example that is also "developed" in (warm) water.
There are lots of possible reasons for inconsistency in a process like
gum, but my experience is that humidity variation is one that people
generally don't think about.
> When it doesn't come out and the image is
> loss the villian sounds like overexposure to me. The gum all hardens
> as the light penetrates even the dark areas of the negative.e
>
> If you are using the sun as a light source (and I do) this time of year
> I avoid exposing prints between about 11am and 2pm. The exposure
> times are in seconds and you have to hover over the print, ready to
> snatch it at whats hopefully the right moment.
>
> If you are using the sun, try morning and late pm.
>
> Gini
>