I may get scolded for this, but here goes: I have much more experience making wine than fermenting feed, but wine making is a process of fermentation. Whenever you ferment something, you are wanting a particular organism to grow in the container. Sometimes the wrong organism gets in there and takes over. When fermenting wine, it has to be carefully protected from contamination or it could be taken over by bacteria. When fermenting feed we want it to be taken over by bacteria, but not just any old bacteria, that's one of the reasons that folks use vinegar, buttermilk, etc. to get the fermentation started. With the billions of different bacteria out there, I don't think it would be crazy to suggest that maybe your FF has been taken over by a bad bug. If I were in your position, I would keep the current batch going, but start another new batch from scratch and be careful not to cross-contaminate the two. Let the new batch ferment for a few days and see if your chickens react differently to it.