When you have too high of humidity the chick will grow too big and at hatch it will be able to pip but is physically too big to zip the shell to hatch and die. Where I am the ambient humidity is naturally too high to use a Styrofoam incubator with any water before lockdown. They (Styrofoam incubators) have a proven history of trapping too much humidity even with the plugs out. Not just here if you research it's a common issue with those type incubators so yes it's proven it is not the best design. People regularly have bad hatches with chicks dying at hatch and by the time they research and figure out what has happened the damage has been done.