Naturally a hen does a better job----we build incubators as best as we can to try and doas good of a job.I've had one chick almost hatch with 50% to 60%, then 70% for hatch. I also had two chicks hatch from my first hatch. But most of my chicks drown or die in the eggs. I seem to find the my hens do a lot better job of hatching egg, then the egg incubator.
Your next hatch drop your humidity way down---even dry incubate if needed---try to stay below 40% but above 20% for the first 18 days then go to 70 to 80% for the hatch. If you got good eggs and your incubator temp is pretty accurate and you turn the eggs like normal----you should see a lot better results. I am a Hands Off Hatcher---so I do not open my incubator for Nothing the last 3 days(add water through a vent hole if needed)---I wait till day 22 to remove the chicks, works great for me with real high hatch rates.