Combine stock, wine, flour, butter, and 1 tablespoon lemon juice in a medium bowl, stirring with a whisk; pour mixture into slow cooker. Sprinkle chicken thighs evenly with 3/4 teaspoon salt and 1/4 teaspoon pepper. Place thighs in slow cooker, skin side down. Arrange potatoes, garlic, and thyme over chicken in slow cooker. Sprinkle 1/2 teaspoon salt and 1/4 teaspoon pepper evenly over garlic and potatoes. Cover slow cooker; cook on LOW for 8 hours.