I tried applying the wax to the teeth of the zipper multiple times and working the zipper back and forth. It's never stuck, it just takes an astonishing amount of effort and makes a larger than expected amount of noise. I've come to the conclusion that perhaps the slider is the culprit rather than the teeth. Haven't had the time to really mess with it much since.
ETA: I've just checked the remainder of the zippers and found two or so that are going back for ones that are less loud and more smooth!