One of my little girls just started limping today. They have free range all day so there is no telling what she did to it. Like yours there is no sign of any kind of injury or anything. She hops around still but all on her left leg. I took her to the coop and set her by the food and water. She ate some and then laid down. I put her in one of the laying boxes so she'd be out of the other chicks' way, but still with the others. Please keep posting anything that you find that helps.