DIAGNOSIS You're overcrowding the basket. The FryForce fan can't circulate hot air properly if food is piled in a thick layer, especially on the bottom.
FIX Cook in smaller, single-layer batches. Shake or turn food at the halfway point. For fries, toss them in a tiny amount of oil (1/2 tsp) before cooking to promote even crisping.
IF THAT DIDN'T WORK Ensure you're preheating the air fryer for 3-5 minutes before adding food. Adding food to a cold chamber starts the cooking process with steam, not crisp heat.
HEADS UP The "4 Qt" capacity is the volume of the basket, not a recommendation for how much food to cook at once. For crisp results, never fill it more than halfway.