Is it possible their ages are not correct? If they are 9 or so months old, they could be going through a minor molt. Missing tail feathers can be many things from molting, to feather picking, to poultry lice.
Yes, I guess I could be wrong on the age however, they are about the same size as our original flock we purchased who are 5-6 months old. Thank you, I will research the poss lice issue!