I use CK royal icing mix from time to time, and it definitely sets hard and pretty fast, as long as you follow the directions on the package (just add 5 Tbsp water and mix). So, I hate to say it, but I doubt the fact that it's royal icing mix (in general) is the issue. Perhaps that particular bag was a bad formulation, but I've never had trouble with CK royal icing mix. I also don't think a smidge of oil on your utensils is going to disrupt setting that much . . . a smidge of oil will deflate a meringue (which is why people tell you to clean bowls when making meringue), but all that bowl-cleaning is overkill, in my opinion, when making royal icing. I use my mixer for many things and never do a vinegar-clean of it before making royal icing. So, my guess is you just got a bad batch of mix or added too much oil-based flavoring to your icing. One reason I prefer to make my royal icing from scratch, starting with raw eggs or pure albumen, is because you always know what you are putting into your icing, and that means more consistent results.