Preheat the oven to 350 degrees F (175 degrees C). Coat a 9×13 baking dish with cooking spray.
Bring a large pot of lightly salted water to a boil. Cook bow-tie pasta at a boil, stirring occasionally, until tender yet firm to the bite, about 12 minutes.
Meanwhile, melt butter in a saucepan over medium heat. Add cream cheese and ranch dressing mix; whisk until smooth. Slowly whisk in milk. Stir in Monterey Jack cheese; cook until cheese has melted and sauce has thickened, 5 to 10 minutes. Crumble 6 slices bacon and stir into sauce.
Combine cooked pasta and shredded chicken in a large bowl. Pour sauce on top and mix until well combined. Transfer to the prepared baking dish. Top with Cheddar Jack cheese and crumble remaining 2 slices of bacon on top.
Bake in the preheated oven until cheese has melted, about 20 minutes.