I agree with
@HollowOfWisps. The first solution I would recommend is slightly higher protein. It doesn't have to be a lot, perhaps 17-20%. As they said, 16% is the absolute minimum for body maintenance and egg laying. If they have ANY other intake that is lower in protein or essential amino acids, that will drop them below that threshold. Any seeds, grains, greenery or fruits they consume will offset minimum essential amino requirements.
A supplement of animal protein (full complement of essential amino acids) 2 or 3 times a week should help.