Get a digital humidity gauge.
Paper towel or just get rid of that substrate and get fresh stuff in there, im reading this like your stuff is moist...like moist moist. If you place your hand on it and you get wet? Then dry that stuff up a little.
Your hide starts getting too moist over the heat pad you can/could get some mold in there.
You get it too moist and your snake could start getting gross scales aka the rot.
You wanna get it 50-69ish
I say 75 tops cause ive had no problems going that high now and then (it happeneds) and ive seen some other dudes who get it around there. BUT I try to keep it between 50-69.
Hope things work out
40 humidity? These arent colubrids.