Lightly grease the inside of your slow cooker with non-stick cooking spray or a thin layer of butter.
Place chicken breasts in a single layer at the bottom of the slow cooker. If very thick (over 1 inch), slice in half horizontally.
Sprinkle the entire packet of dry ranch seasoning evenly over the chicken breasts.
Pour buffalo wing sauce over the seasoned chicken, then pour chicken stock around the sides. Place butter on top.
Cover and cook on LOW for 6 to 8 hours or HIGH for 3 to 4 hours until chicken shreds easily and reaches 165°F (74°C).
While chicken cooks, whisk ranch dressing, mayonnaise, and apple cider vinegar in a small bowl. Toss with coleslaw mix, season with salt and pepper, then refrigerate until serving.
Transfer cooked chicken to a cutting board and shred using two forks or meat claws. Return shredded chicken to the slow cooker and stir into the cooking liquid.
Add about 1/4 cup (60ml) of cooking liquid back to the chicken if needed to keep it moist. Let rest on WARM for 15-30 minutes to absorb more flavor.
Preheat broiler to HIGH. Split buns and place cut-side up on a baking sheet. Top with provolone cheese and broil 1-2 minutes until cheese is melted and buns are lightly toasted.
Pile shredded buffalo chicken onto the bottom bun halves, top with ranch coleslaw and blue cheese crumbles if using. Place the cheese-topped bun half on top. Drizzle with extra buffalo sauce or ranch dressing and serve immediately.