I'm not sure if you mean the topping stiffens up and becomes chewy as it cools - which would be normal - or whether it becomes crunchy like hard candy. Here is the recipe I use for my caramel rolls, which has never become crunchy for me. The ingredients don't sound very different from yours, so this may or may not help you. I hope it does.

CARAMEL ROLLS

1 recipe of cinnamon rolls, unbaked
1 1/3 cups packed dark brown sugar
1/2 cup butter
1/4 cup light corn syrup
2/3 cup chopped pecans

Cook and stir brown sugar, butter, and corn syrup till smooth and combined. Divide between pans. Sprinkle with pecans. (No need to grease pans.) Place cinnamon rolls over caramel in pans. Bake in preheated 375F oven about 20 minutes.