Trim any extra fat from roast, cut roast into 2-inch pieces. Place beef, sweet potatoes, onions, apples, beef broth, garlic, salt, 1/2 tsp. thyme and pepper in slow cooker.
Cover, cook on low for 8-9 hrs. Transfer beef, sweet potatoes and apples to lg platter, keep warm.
Let liquid stand 5 min for fat to rise, skim off fat. Combine cornstarch, remaining thyme, cinnamon and water; stir into liquid. Cook 15 min or until juices are thickened. Serve sauce with beef, potatoes and apples.