Are some of your birds too thin?
Birds that are too thin are high risk to die during the molt. It is important to provide special conditions for thin birds that promote weight gain, just gaining a few grams can restore their health and save their life!
Separate out thin birds from medium or heavy birds and group the thin birds in as few per cage as possible. Then place numerous perches and extra feed dishes and water that are easily accessible to the birds so that birds will hop around rather than fly.
Watch the birds to determine how many perches are necessary. In my breeder cages, four perches place in the lower middle level of the cage keeps them hopping but still avoids letting them hanging on the wires. If they hang on the wires, you will have to raise the perch level.