Molt doesnt occur all at once with every bird. There are different types of molt; some birds might have a mild molt where they lose only a few feathers and may not even be recognized as a molt. Others might lose all their feathers and become almost completely naked. Molt varies from bird to bird. Stress can trigger a molt anytime of the year.
Additionally, it takes time for fluff and feathers to regrow, they just dont grow out in a few days time.
If you dont see feathers on the ground when birds are molting, it means birds are eating them, indicating they need more protein in their diet. It would be best to provide them with gamebird feed which has a higher protein content. Give it to your birds during molt and then slowly wean them back to regular layer feed once they're out of molt.
Another possibility are feather pickers. Identify which birds are feather picking, then you can put peepers on them or cull them. Pecking order problems can be taken care of with peepers as well.
If you have a rooster, he can cause feather loss/damage. A chicken apron/saddle will protect a hen, or put peepers on the rooster.
When inspecting birds for external parasites, always closely inspect the vent area where it's warm and moist. Inspect feather shafts for attached lice/mite eggs.
