Molt usually occurs when feathers fall out. In your picture, the feather shafts are in place, but the vane seems to be missing. I have seen my chickens molt, sometimes heavy, and sometimes light.
I never had such a situation occur in my flock in well over 20 years, of chicken keeping. I would check hen over well and see if there are any possible parasites on those feathers.
Is it possible that chicken is self preening, and possibly removing the vane portion???

I heard of feather mites, but only seen them on some pigeons a friend was raising, and that was very long ago. Not sure if that may be something you are dealing with.
Lets see what others may comment on those feathers. I'm interested to find out this cause.
WISHING YOU BEST,,,,,,,,,,,,,,,,,,,,,,,and