Air cell not big enough

Is there some reason why eggs from one particular hen would fail to develop a big enough air cell? The humidity in my incubator seems to be working great for the eggs from all my other hens. Of the eggs that developed and made it to lockdown, all of them have hatched except for the ones from this particular hen, and those seem to have very small air cells when they go into lockdown. They've been incubated under the same conditions as the rest of the eggs, so I don't think it's because the humidity is too high. And the shells on those eggs don't look extra thick or anything. The chicks develop and I can see them moving when I candle at lockdown, but they die somewhere after that and never pip. Any thoughts?

She definitely fertile. There's a fully formed chick in there, I checked after the first one failed to hatch. The shells seem normal, so maybe it's something to do with the membrane, like you say.

I think I've decided it must be a shell thickness issue. I finally got one egg from this hen to hatch, and it was a very porous looking egg when you candled it so I think the shell much have been thinner than her normal. All of her other eggs develop but never even pip. Now I just have to figure out if it's a diet issue or if it's just part of her genetics to lay very thick eggshells.