Using Sugar Bean’s stand mixer macronage recipe, they visually look nice but are hollow… tips?

So I did Sugar Bean’s recipe for Macs using a stand mixer for the macronage. I did the oven drying and that did indeed help form a skin quick.

Visually I’m happy with the outside, but inside they’re hollow. Any advice on what this may indicate? A few spots on the tray where the Mac was just ever so slightly wet on the bottom (barely, but I did have one or two that stuck slightly to the mat when I went to take them off.)

As far as this style of making them, I really like it and I’d love if I can make this way work! Did I not beat the eggs long enough, or over/under macronaged it, oven temp issue, etc?