DIAGNOSIS: You are overloading the basket. The compact 4QT basket has a smaller effective cooking surface than you think. Air cannot circulate.
FIX: Cook in smaller, single-layer batches. Do not stack or pile food. Shake the basket vigorously halfway through cook time. For frozen fries, a max of half the basket is the real limit. Dry food surfaces with a paper towel before cooking. Ensure temperature is set to at least 380°F for crisping.
IF THAT DIDN'T WORK: The heating element may be degrading. Test by cooking a single piece of bread at 400°F for 3 minutes. It should be very dark and crisp. If not, the heater is weak.
HEADS UP: Adding a light spray of oil (not aerosol non-stick spray) to starchy foods is necessary for the "Hi-Fry" technology to work effectively. It's not magic.