Yeah, I would assume differences in the make up of the colony. Differences in ages of bees. Differences in amount of adult bees/brood ratios. Maybe equalizing brood between all of the colonies would even out the production of comb.Smaller amount of wax makers? Illness? Some other reason?
A couple of my hives are just a little slower than others in terms of drawing out frames, even though they've all been fed syrup for the past little bit.