Sorry to bust in on a pro thread, but I am an air conditioning tech and I have refrigeration education.
There might not be a simple solution, but here's one thing to try: make sure the air circulation is ok in there. If it's crowded with stuff, it can't cool it all--not so much because of the amount of stuff, but because the cool air won't reach every part of the fridge. Also because the temperature control is only reading the temperature in one certain location, and if all's cool there, it won't turn on the cooling.
Make sure the cooling from the evaporator coil (the inside coil) is not blocked off from the rest of the fridge somehow.
Also, make sure the doors are sealing well.
There are other things that could be happening, of course, but I'd suggest checking these out.
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