Freezer not freezing correctly

I have a GE profit refrigerator/freezer. The user interface displays the actual temp of the freezer as -9*, but the actual temp is 20*. I have replaced both thermistors and the control board. It is still doing it. I can put the user interface into test mode and everything tests normally. I set it to prechill mode and it will get to the correct temp in the freezer, and read the correct temp for a while. But ultimately the user display will go back to registering -9* as the actual temp but it will only be 20*.

Also, there are no leaks in the system. The coolant levels are normal. Does anyone have any ideas?