I am not sure where you live but i found for myself living in michigan i do not need to add any water to my imcubator at all. The ambient humidity is enough all on its own, even if i keep my incubator at 25-40% humidity i get all wet chicks drowning in their shells. So i know keep my incubator at 37.5C and add no water...on day 18 they go into the hatcher with 50-60% humidity. That is what has worked for me, you will have to find what works for you. There is no right anf wrong way to incubate, it all depends very much on where you live. So if you have problems just come back to the forums here and ask fro some advice..it took 4 hatches for me to figure out what i was doing wrong.
How are you measuring the humidity? I have up to 25% difference in gauges. Last 2 hatches of about a dozen eggs, I had 2 or 3 to hatch normally and the rest close to fully formed dead in the shell with lots of slime around them. Assumed they drowned. Have a batch not going and keeping the humidity really low. Weight loss after 14 days is 13-14%, seems sort of high according to the threads. Using a hatcher that I will keep the humidity about 70%. Will see what happens. Not sure what the autopsy of too low a humidity looks like???