That sounds promising
Chick starter does have more protein than layer feed, so it is possible that they needed the extra nutrition.
Once they recover you may want to consider feeding an all flock/flock raiser to all your chickens since you have a mixed flock (boys/girls), just offer oyster shell free choice for your hens.
I have a cockerel and hens and use a flock raiser and so far no problems. I do like the extra protein so I can give treats like sunflower, corn, veggies and fruit and not worry about decreasing nutritional intake.
Just a thought.