Do you have a lid? A slightly vented lid will greatly help the humidity levels. Some people use a sub straight like coco fiber since it holds humidity quite nicely. Yet I personally don't use a sub straight since is just one more thing to clean/replace when you clean your dubia bin.
I have cut out 90% of the lid and replaced it with screen I was just wondering because I think I used up all my small nymphs lol and now I am waiting on new births to feed my young Chams. I was just wondering if they were not producing due to humidity. I noticed I have at least 5 or 6 adult females and 5 adult males but a TON of nymphs of which I can not tell which sex they are lol.
Humidity (low) usually just causes molting problems. They only give borth ever 1-2 months, so you might have to wait a while. Feed them well and they will keep producing very quickly with heat. I just put a lid with no holes on my tubs and open them once a day for some air. They produce better for me like that.