They eat if they are hungry; they don't if they are satisfied. The tricky part is working out what exactly they are hungry for, if they are hungry.
They have one dominant appetite, for protein. They can make protein out of carbohydrates if necessary, but that requires them to overconsume carbs in the process. And meanwhile too much protein is not good for long term health. So the easiest and safest way to ensure that your birds are getting what they need on the protein / carbohydrate matrix is to supply appropriate foods separately, so they can choose individually whether to fill up on high protein food or high carb food. Try putting out a bowl of meat or fish or insects or dairy alongside the fermented feed; how they consume that will indicate whether and to what extent they are each hitting their protein target.
They might alternatively or additionally be hungry for a micronutrient or two (vitamins and minerals) but that would probably be met by the animal/ fish/ insect/ dairy you offer in addition to their regular ff.