A better question might be "what is causing it" or "how can it be corrected".
If the condenser at the back and/or underneath the fridge can not get rid of the heat from the refrigeration process, the center mullion area between the doors will get extra hot. (It's always warm when running to prevent sweating.). Your symptom is either caused by a dirty or plugged condenser or the condenser fan motor not functioning... or both.
The condenser should be *thoroughly* cleaned several times a year, or seasonally or monthly if you have pets! You might as well do that now while you're checking operation of the condenser fan motor at the back. The condenser fan should be running whenever the compressor and inside evaporator fan motor are running.