Place the chicken pieces and frozen vegetables in the crockpot.
In a separate bowl, whisk together the cream of chicken soup, cream of celery soup, chicken broth, milk, garlic powder, onion powder, thyme, salt, and pepper.
Pour the soup mixture over the chicken and vegetables in the crockpot, and stir to combine.
Cover and cook on low for 6-8 hours, or on high for 3-4 hours, until the chicken is cooked through and the vegetables are tender.
In the last 30 minutes of cooking, add the cooked biscuit pieces to the crockpot and stir gently.
Serve the soup hot, garnished with additional cooked biscuit pieces and fresh thyme, if desired.