This phenomena is well known to those of us who live in old, less well insulated houses. As the outside temperature drops, so does the temp of the house wall. The objects inside the house now lose more heat to the wall. However the temp of the very small area where the thermostat is located remains warm enough for the stat to not call for heat. This is why modern houses have supply runs located near outside walls as well as having better insulation.
While in the fridge the heat is moving in a different direction, the physics are the same. Increasing the insulation of the cabinet and perhaps providing some air circulation inside the fridge to even out the inside temps may help mitigate the problem.
