Just looking for a direct answer for this question, changed my recipe to use kaolin clay rather than cornstarch and now my bombs flatten. I'll try to keep them in the molds but then they get stuck in the mold if I'm not continuously taking them in and out of molds while they dry. I also switched from water to witch hazel and halved my epsom salt amount. I also dont pack my molds super hard, should I pack harder or what actually causes them to flatten, moisture or air in the bombs?? Please and thank you! I also think maybe moisture is an issue, I put in cold garage and they did well not sticking to molds, they were in garage drying for 7 hours and then I brought them inside and they sat over might and now are glued to molds