My freezer section was icing up to the point that it couldn’t maintain below 40. I realized that my keg box was just wayyyy too big for a mini fridge so I got some of the pink thick foam and a wooden frame and basically filled in about half of the keg box. Now it can hold either 2 1/6kegs or 1, half keg, plus CO2. I had to struggle with this so hopefully this saves someone time in figuring out how to fix a similar problem.
You may want to take another look at your air flow. I have a small Haier fridge and can get the box below freezing with 2 sixteen gallon kegs. Place one fan in front of the freezer with air flow blowing toward the kegs, If thats not enough place a second fan on the opposit end near the floor blowing towards the fridge to create a circular flow. Hope this helps.