Season the beef chunks with salt, pepper, and smoked paprika. Heat a large skillet over medium-high heat and brown the beef in batches until it has color on all sides. Transfer the beef to the slow cooker.
Add the diced onion and minced garlic to the same skillet and cook for 2 minutes until the onion starts to soften. Scrape the mixture into the slow cooker.
Add the quartered mushrooms, barbecue sauce, beef broth, Worcestershire sauce, and brown sugar to the slow cooker. Stir everything together.
Cover and cook on low for 8 hours or on high for 5 hours until the beef is fork-tender.
Stir the stew once more before serving to distribute the sauce.