DIAGNOSIS The presets are generic starting points. They often underestimate for thicker or frozen foods. Your unit is not broken, it's undercooking.
FIX Do not rely solely on presets. Use the 'Power' button to set a higher temperature and the 'Time' button to add 5-10 minutes. For chicken, always use a meat thermometer to verify 165°F internal temp.
IF THAT DIDN'T WORK The temperature sensor could be reading inaccurately. To test, run the fryer empty at 350°F for 5 minutes. The air inside should be very hot. If it's barely warm, the sensor is faulty.
HEADS UP Never cook frozen, thick-cut meat using just the preset. Always add time and verify temperature. Food safety is more important than the preset label.