Diagnosis
Porous silicone has absorbed oils and odors. Dish soap and water cannot remove them.
How to Fix It
Remove the gray silicone sealing ring from the lid. Soak it in a mixture of warm water and white vinegar (50/50) for one hour. Scrub it with a soft brush. Rinse. If odor persists, make a paste of baking soda and water, coat the ring, and let it sit for another hour before rinsing.
If That Didn't Work
The ring may be permanently saturated. Replacement is the only option. The part is often called the "Lid Seal" or "Gasket." Contact Ninja for part #TB301LS.
Heads Up
Do not soak the entire lid assembly. Only remove the silicone ring. Do not put the lid or ring in the dishwasher, as the high heat can degrade the silicone and trap odors worse.