Was your deflector plate metallic?
Deflector plate - use a fire-friendly ceramic/fireplace brick/pizza stone; not metallic.
Place the drip pan on the (stone) deflector plate... retains the mess and eliminates flare-ups.
Cooking at Mason-Dixon BBQ Services
Lang 84 Deluxe Kitchen known as "The Glamazon" , Custom Klose Backyard Chef... of Snot, and a 22.5 WSM
Lang 60 Mobile - The Damsel II, Lang 48 Patio - The Damsel, Bubba Keg Grill - RIP, Double Barrel Smoker and a BSKD