Combine corn muffin mix, eggs, milk, and 4 tablespoons maple syrup in a 4- to 6-quart slow cooker until well blended. Stir in the sausage, scallion, and apple until all of the chunks are evenly distributed. Cook on low 3-½ to 4 hours. Spoon the remaining 2 tablespoons maple syrup over the top. If your slow cooker has a warming setting, you can keep the cornbread warm several hours; if it doesn’t, the cornbread will stay servable up to 1 hour with the cooker turned off. Cut into squares or wedges to serve.