Diagnosis
You're overloading the basket. Air needs to circulate under the food. Moisture from overcrowded food pools on the crisper tray.
How to Fix It
Cook in smaller batches. Use a single layer. Shake or turn food halfway through cooking. For wet items like french fries, pat them dry with a paper towel first. Ensure the crisper tray is correctly seated in the basket.
If That Didn't Work
The fan might be obstructed. Unplug the unit. Look inside the top heating chamber for large debris blocking the fan blades. Also check that the rear air intake vents are not covered by a wall or cabinet.
Heads Up
Never use parchment paper or liners that completely cover the crisper tray holes. They trap steam. Use perforated liners or cut your parchment to fit just the basket center.