I had encountered shellac gone bad before, but I had never come across shellac that won't dissolve completely in denatured alcohol.
I mixed up a batch of blonde shellac but, days later, it looked like semi-masticated lemon jello rather than clear finish.
I mixed another batch using amber flakes to see if the alcohol was the problem, but they dissolved completely in an hour.
I had used flakes from the blonde bag before. I couldn't understand why they would have gone bad because they were always stored in a cool, dry shop.
A quick google search led me to a blog post written by Joel Moskowitz, so I emailed him to ask his opinion.
He told me that the flakes had oxidized and that they should have been stored in an air-tight container (rather than in the original plastic zip-loc bag). He also suggested that I try pulverizing the flakes, but I had already tried that and it didn't seem to help.
Today I bought a brand new bag of blonde flakes and immediately poured the contents into a glass jar with screw-on lid.
So, if after 24 hours your newly mixed batch of shellac still looks like gatorade-doused caviar, you know what to do.