By any chance, do you know the mill date of the feed your BO is not enjoying? The quality of ingredients in feed deteriorate somewhat quickly so if it's stale or old (not really talking about expiration date), they'll possibly look for a better alternative. This is something I've learned here, and there is a lot of information on this. I agree with the above poster, leave the scratch out completely. It might be a good idea to offer the oyster shell in a separate dish on the side as free choice, instead of mixing it in. I know that my pullets do better on higher protein feed. The like Purina Flock Raiser which is 20%, I believe. The Grower feed I purchased was 16% and they weren't fans plus they started eating feathers (which could suggest they need more protein).
@Kiki is really amazing at this feed/nutrition stuff
Also
@EggSighted4Life is another one that really knows her stuff