Lightly spray the inside of the crockpot with non-stick cooking spray.
Add shredded chicken, cream cheese, ranch dressing, buffalo sauce, and 1 1/2 cups shredded cheddar cheese to the crockpot; gently stir to combine.
Place the lid on the crockpot and cook on low for 2 1/2 to 3 hours.
30 minutes before cooking is done, lift the lid and sprinkle remaining 1/2 cup shredded cheddar cheese on top; replace the lid and cook for remaining 30 minutes.
When finished, top with blue cheese crumbles and sliced scallions if desired.
Serve the dip warm with tortilla chips, cut veggies, bread, or crackers.
Keep warm in the crockpot during serving, then store leftovers in an airtight container in the fridge for up to 5 days.
Reheat in the microwave in 30-second increments until hot.