Humidity is key to keeping most cuttings alive (this years green growth, hardwood cuttings are a different game). They need to take in water through their leaves while they dont have roots. However, too many leaves and they will lose too much water and die as well. So really you only want a couple leaves on your cutting, then keep it fully enclosed in a plastic bin or something similar. As close to 100% humidity as you can get will provide alot of success. Then. put it outside in the shade. Direct sun will heat the bin up too much and kill the cuttings. Somewhere like the north side of a building works well, you get blue sky overhead to provide light but only very limited direct sunlight to heat things up too much. Using a clear container to propogate in will show you when the plant has rooted so you dont need to pull on things.
I know you said you are doing the humidity thing, so I would wager part of your problem is your transition from the humid environment to outside. I have found when I take my rooted cuttings out of the bin, if I do it in 1 day, they all die. Basically 100% failure rate. Instead, over the course of 1-2 weeks (depending on how humid it is outside), I open the bin slowly. Day 1-2 just a crack, then a little bit more every day or two until the bin is about 1/4-1/2 open. Then its enough to move the cuttings to open air but still in the shade for a few more days until they can get into some sun. I have gotten extremely high success rates on nearly every deciduous species I have tried with this method.
If you have more questions, look up Mike Kincaid on youtube. He propogates alot of Rhododendrons and figs, but his process works for most things.
