Humidity can cause problems with your mproyal icing. I don’t care for Wilton meringue powder. I recently changed to genies dream meringue powder, which I buy from creative cookier. I use her recipe and it always works well. Also, I always clean my bowl, beater and utensils every time with vinegar. Any amount of fat can ruin icing. The vinegar takes care of that problem. Hope it helps.