I have used this method with every mantis I have ever kept. Not saying it doesn't happen but I think if that caused issues it would have been apparent by now. I have a mismolt every now and then like everybody however these are just different in the way that they tend to get stuck at the middle of the back legs. Out of six nymphs three have molted with this issue.The spagnum moss in the bottom may be your problem. Long-term high humidity without airflow causes mantids to lose more internal moisture through respiration which can cause them to dehydrate rapidly with minor drops in the humidity. Sprayed water should dry up within a short period and it increases hydration (they can drink it) without causing an unsafe humidity.