Poor molting surfaces can result in falls, especially in later instars. Sticks, bark, and other natural surfaces are good options, and foam shelf liner is too. When mantids molt and suspend themselves from the old skin, it can break (this is often the cause for failure of Idolomantis). What they need is something in front of them as they're hanging there drying.
In nature, mantids typically molt late night/early morning when humidity is high and temps are cooler. I always tell people to do hi temp/room humidity daytime with 68-70F/high humidity (sprays and/or fog) nights.