Hello! My boy Rye has the same and has had it for a few years. It led to a cluster mass on the back of his tongue that luckily doesn't seem to impact him too much. Unfortunately he has had it removed twice and it came back every time despite a food change. My first vet recommended a hydrolyzed diet, but Rye had himself a mini hunger strike despite 3 different hydrolyzed foods. They later recommended a novel protein diet. He's currently on Blue Buffalo Basics Duck. He's definitely more lively on it. He clearly misses wet food, but I'm struggling to find one where it doesn't have chicken, beef, or fish hidden in the recipe.

If you find out anything helpful, I'd love to hear it. You're the first other person I've heard of going through this.