I just added 6 Pullets in my Flock and have stopped all snacks till these Pullets find the feed and water. All is going great they are eating and still healthy in my flock
Well...Each bird is an individual so if that one chick only was consuming things it liked and being you have lots of birds its possible it wasn't eating the proper nutrition daily.
Stop all extras for two weeks and only provide balanced feed from a supplier.