Several conditions are increased with too high of humidity. Splayed leg for one but it's second to too high of temp causing that problem. Really the biggest thing about humidity is controlling the amount of water/weight loss of the egg. Somewhere in line of 12% mass should be lost during incubation and this is water evaporating from egg. Higher humidity lowers evaporation from egg and low humidity increases it.
Fast forward and easier way to monitor is to candle the egg and look at the air cell. Adjust humidity if needed to grow the air cell to proper size. You'll find 30% RH will do the trick to day 18 then up humidity to what you want for hatching, I prefer 70% RH. Make sure to preform a salt test on hygrometer to calibrate it.
This is a decent diagram of air cell growth by day. It's not exacting, every egg is different (more or less porous) but in general terms a fair reference. Smaller than what shown here for day 14 on hatch would increase mortality due to drowning in shell on internal pip. Air cells smaller than day 7 shown at hatch is complete death sentence. Ask me how I know? We all started hatching at one time. It's a learning process.