very difficult to say without seeing the bird ,, this is really just a guess, birds that have had paramyxovirus and came through it are usually left with some sort of impediment ,, much the same with paratyphoid [salmonella] not usually good to breed from,,,,,,off course it may have nothing to do with this at all , so maybe best advice would be good avian vet,,,, its possible the bird has been hurt in some way , sometimes bruising on the wing takes a while to heal