From the information you have now provided, your flock's diet may well be the issue. Your bird could easily be suffering from a vitamin deficiency. Scratch is not a complete food and it is designed to be given as a treat scattered on the ground to encourage "scratching" so that they work for the calories it provides. Feeding scratch grains ad lib from a feeder is like giving kids fries every day. There is no balance, a lack of vitamins and essential amino acids and will most likely make them obese and at risk of fatty liver syndrome. Hens will be more prone to reproductive disorders like prolapse and salpingitis and possibly internal laying.
I would strongly encourage you to start using a formulated feed, either grower/all flock or layer (depending on your flock's age and gender mix) and cut the scratch from their diet completely for the time being at least. They would also probably benefit from a good quality poultry vitamin supplement for a week as well, particularly the one with issues. Be prepared for your chickens to go on hunger strike but you need to instigate tough love to ensure their health into adulthood.