Cook bacon in a large skillet over medium heat. Remove and drain on paper towels.
Add, onion, carrot, and celery to the same skillet; cook and stir until beginning to brown, about 5 minutes. Add garlic; cook and stir 1 to 2 minutes. Transfer vegetables to Crock Pot. Add 1 tsp oil to skillet. Add mushrooms; cook and stir until beginning to brown. Add to Crock Pot.
Heat remaining 2 tsp oil in skillet. Brown beef and pork over medium-high heat, stirring to break up meat. Drain fat. Transfer meat to slow cooker. Stir in bacon, tomato puree, beer, broth, tomato paste, salt, black pepper, and red pepper flakes. Cover; cook in a Crock Pot LOW 8 to 10 hours.