Ray
The stem of the feather is called the rachis (RAY-KISS) and the herlis the barb. Coming off the barb are the barbules which lock the barbs together on ordinary contour feathers.

Good herl has barbules on both sides. If you look closely at your herl you will likely see the barbules on the bare side of the barb are just very stunted.

Diet is probably the main culprit.
art