I can't answer your question as a soap maker, but as a chemist I can.

I can understand it not to work well in rainy of humid weather because lye absorbs moisture from the air. So the more humid it is, the more the lye will prematurely react.
I know that when I was working in the lab at school, when we worked with lye, we had to weigh it quickly, because if we waited, the weight would increase.
I also noticed the lye crystals turned kind of greasy looking, because of the water that reacted with it.