I have a side-by-side fridge…the freezer is fine but the fridge side is warm and yes I do have frost build up on the inside back wall of the freezer
If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.
check , defrost heater, defrost thermostat. Here- http://www.acmehowto.com/howto/appliance/refrigerator/refrigerator.php
If they check out ok the defrost control board will be the problem. Double check your model number as it didn’t have any matches looking for diagrams.