Diagnosis
Mechanical damage from metal utensils, abrasive cleaners, or stacking/scraping the plates. Damaged coating is a consumable wear item.
How to Fix It
Stop using the damaged plates immediately. Order genuine Ninja replacement crisper plates (part number usually on the underside of the plate). They are sold as a set. Use only plastic, silicone, or wooden utensils. Hand wash with a soft sponge.
If That Didn't Work
If replacement plates are not available, you can use the baskets without the plates, but food will not get as crisp and cleanup is harder. Do not use third-party plates not designed for this model. They can affect airflow and cooking performance.
Heads Up
Ingesting flaked non-stick coating is not toxic, but it is not intended for consumption. A severely damaged plate can also cause uneven heating and hot spots. Replace it.