Diagnosis
Plastic, especially the silicone seal in the lid, absorbs odors. Dish soap alone won't remove it.
How to Fix It
Disassemble the lid completely. Remove the silicone sealing ring. Soak all plastic and silicone parts in a solution of 1 part white vinegar to 2 parts warm water for at least an hour. Scrub with a baking soda paste. Rinse thoroughly and air dry.
If That Didn't Work
For persistent smells, use a denture cleaning tablet dissolved in warm water. Soak the parts overnight.
Heads Up
Do not soak the lid assembly with the silicone seal still installed in its groove. Food particles trapped underneath cause the smell. Always remove and clean it separately.