Place chicken, broth, Dijon, thyme, salt and pepper in a 5-quart slow cooker. Cover and cook on low for 2 1/2 to 3 1/2 hours, checking chicken from 2 1/2 hours and removing pieces as they reach 165°F.
During the final 20 minutes of cooking, add ham to the hot broth and heat it to 165°F. Transfer chicken and ham to a covered serving dish and strain the cooking liquid.
Melt crumb butter in a small skillet and toast panko over medium heat for 3 to 4 minutes until golden, stirring often. Set aside.
Skim fat from the cooking liquid and measure exactly 1 1/2 cups, adding only as much of the additional 1/2 cup broth as needed to reach that amount; reserve any excess. Melt sauce butter in a saucepan, whisk in flour and cook for 1 minute.
Gradually whisk the measured cooking liquid and milk into the flour mixture. Simmer for 3 to 4 minutes until smooth and thickened, then switch off the heat and stir in Swiss until melted.
Fold chicken and ham into the hot cheese sauce. Divide among 6 servings and add the toasted crumbs evenly just before eating.