For what it is worth - Bailey had some mouth sores before she was put on a steroid and we changed to hypoallergenic food. So I would lean towards the food intolerance/allergy possibility. She didn't have anything on her neck, but little bumps between her eyes and ears. But if I've learned one thing on this journey it is that every cat is different. Hope you find a solution. It is hard to see them in discomfort.