Is it Often that Mantis will have a bad moult?

After reading through lots of posts on the forum I have come across threads about Mantis that are deformed or have health problems due to a bad moult. Is it often that Mantis will be deformed after it's moult or is it due to problems in the tank such as infection, humidity levels ect. I am a bit worried as I have no Heat mat for my mantis cage and we are approaching Winter now so the Temperature will drop, it's normally about 27c in this room but during the winter this can drop. If I do buy a heat Mat where would I put it? does it sit under the Substrate or does it stick to the side of the tank?

i have mine under the substrate

i'm on my first mantis so i'm not sure about the bad moults myself

Bad moults can occur due to a number of reasons, it can be because of food shortage, getting entangled in it's own shedded coverings, or it might struggle to get loose from the old coverings and tear off a limb by accident.

One of my mantids died from being deformed as he was stuck in his old skin and could not get out. I tried holding the crickets in front of his mouth so he could eat but he never did and died of starvation.

You can have the heatmat on the outside of the tank at the back, at one end so the mantis can choose which temp he prefers, put a polystyrene tile over the mat so all the heat goes inside.