I feel that I have to defend the product.
Yes, I had this problem through two changes of GFCI units.
Yes, the problem seemed to resolve when I followed my electrician's suggestion re humidity and "aired out" the unit for an hour before lighting off.
BUT, in the 4+ years since I moved into my new house the problem has not recurred.
I have owned my SM-45 for over ten years. It sits outside under a canvas cover through all kinds of New England weather and, except for a handful of instances of this problem, it has been 100% reliable.