Well, I know it's probably just coincidence, but I just checked the hisser bin and I saw approx another 40 nymphs huddled up and around momma! Woot woot!!
I just bought those extra 10 hissers a week or so ago, added some substrate along with wood and cork hiding logs and bam! Oh, and I've also been misting (occasionally) the walls to up the humidity!
Like I said, probably coincidence, but I have baby hissers again!