Sour crop in a whole flock.
Do you suddenly have long green grass growing? Have you fed any treats lately that might have clogged up the crops? Smell and look at your feed and corn to look for mold. I would stop the corn, and put water with ACV with the mother and a little plain yogurt in their feed, stir it in a big pan, and make it very thin. Then massage crops of those with doughy or hard crops. I have never had crop problems either, and just this past week lost one to impacted crop and gizzard, and helped another with sour crop. Feel of the crops first thing in the morning before they have eaten to see if they have gone down. Here is a good link to read: