It is not enough cold enough inside the appliance
The temperature is set too high.
Too warm goods has been stored .
Too much food has been stored at one time.
The goods are too close each other.
A door of the appliance is not tightly closed.
The door has been opened too frequently or for too long.
Reset the temperature.
Always cool down goods before storing them.
Always store small quantities of food.
Leave a gap between several foods allowing air flowing.
Close the door.
Do not open the door too frequently.