If you're giving both FF and sprouts, it's not surprising that they show a preference for sprouts. What if you tried giving them their FF in the morning, and gave the sprouts before they go to roost?
ReillyJ: You might want to cut back on the amount of FF you give them until you find an amount that they will completely clean up. I give my girls a good feeding in the morning, enough that their crops are all filled up, and the FF is gone by 10 AM. This ensures that the bully's get their fill, and there will be plenty left for the bottom pecking order girls before it's all gone. Then, they get a feeding of dry feed before going to roost. This later feeding ensures that their crops are not empty at roost time, and keeps them expecting something from me at bed time to make them easier to handle. Not a good idea to leave any kind of food out at night. It will attract pests.
Island girl: I hope your production picks up. FF shouldn't be any part of the issue. Did you by chance change your feed brand? My girls have dropped from 11/16 to 8-10/15.