Too high a humidity is my prime suspect in sticky hatches. Both too high and too low are problematic. Best is to follow the air cells against charts for the species you are hatching. The "right" amount tends to be lower than what the manual calls for. At hatch, though, from first pip to completing the zip, needs to be pretty high, 60-70% work best for me. The more eggs I have to hatch, the more I find the last to hatch that have been exposed to higher humidity for too long tend to be stickier than the first or middle of the hatch.