Oh, than it might take me sometime to find about, I've had chickens since about 2018/2019 , so if my information is wrong, please feel free to correct me!
I don't know if someone already said this, but maybe they're lethargic? I can't really tell but, my chicken Caramel had this happen. Did you see anything in their feces? If their is mucus and/or blood, I think I can figure it out. Reply back if her feces had any mucus or blood, I'll find out.