Freezer not freezing, fridge works fine
We have the same brand and it is a PITA. It needs to keep the air moving inside the case. If the air does not circulate it will create the problem you have. There is in ours, a charcoal filter that needs to be changed every 6 months, otherwise it restricts the airflow. Items inside the fridge part needs to be away from the back wall and the filter so air moves.

The logic is, yes the fridge part is cold enough, the struggling freezer part can maintain the 38 or so degrees to keep the fridge proper, but without circulation, the freezer can't do what it needs to get down to 0 degrees. 

If yours has a charcoal filter remove it and the temp should return to normal. It will cause no harm, I had to do it myself and I ordered filters online to replace it.