we have 12 hens. 10 are 18 months old, 2 are 6 months old. The older ones molted this spring and eggs production dropped by about 2/3. Then gradually built back up. some feathers fell out, and did not fully regrow. Now ALL egg production of ALL hens shut off, almost overnight. Even the 6 month olds, for about 2 weeks now. They are eating, drinking, pooping normally, bedding and nest boxes get regular cleaning, diet is laying crumbles, scratch, flax seed, oyster shell, and occasional treats. Daytime and nighttime temps are normal. What could be going on??