Diagnosis
The lower heating element or its reflector plate is not activating properly, or food is blocking the lower air intake.
How to Fix It
First, ensure you are using the 'Dual Blaze' or similar high-heat preset that activates both top and bottom elements. Check the bottom of the cooking pot. Ensure the circular air intake holes are not clogged with food debris. Clean them with a pipe cleaner or soft brush.
If That Didn't Work
The lower heating element may have a faulty connection or be burned out. Visually inspect it through the holes in the bottom of the pot. You should see a coiled element. If it looks damaged or doesn't glow during preheat, it needs replacement.
Heads Up
Do not use parchment paper or liners that completely cover the basket bottom. They block the crucial upward airflow from the lower element. Use a perforated liner or none at all.