DIAGNOSIS High humidity is getting trapped inside. This happens when you open the door frequently in a humid room or put in room-temperature drinks that "sweat."
FIX Reduce how often you open the door. Set the temperature a bit higher—condensation forms more easily at the very coldest settings. A small container of baking soda inside can help absorb excess moisture.
IF THAT DIDN'T WORK Check the door seal for leaks (see previous fix). A leak allows warm, moist air to constantly enter, which then condenses on the cold walls. Also, ensure the drain hole at the bottom of the interior back wall isn't blocked by debris.
HEADS UP Some light condensation or frost on the back cooling panel is normal during high humidity. Puddles of water at the bottom are not. If you see puddles, the internal drain is likely clogged.