One more thought: How long is Corny? You mentioned feeding him a large mouse in your first post, & most corn snakes do not need that much food,
it makes them fat. It is possible that you've been feeding too much? You also mentioned the vet said 'no' to large mice but suggested, if I recall, that
instead you offer him 2 smaller ones? But that can do the same thing...possibly too much food. Offer one smaller mouse per meal.
How often are you feeding him? As an adult snake of 5 years, I'd feed him about every 10 to 14 days. (from your earlier posts I thought he was younger?)
And remember that there's no delivery service in the wild...snakes do not require an exact feeding schedule...that's only our doing.
What would really help here is a photo showing Corny next to a sample of the 'large' mice he's been eating. Especially since "large" means different things
to each person. It's possible that you've been over-feeding & that's why he just doesn't want to eat yet. I hardly ever weigh my snakes, btw: unless I
need to calculate a dose of medicine or there is a serious issue of weight loss, it's not needed & can stress some snakes.