Thank you for the information, that helps a lot!
What is most likely going on is frost build up behind the back panel of the freezer that is not being eliminated by the defrost cycle.
Every 8 hours or so a heater will come on for short period of time to melt the frost on the evaporator (cooling coils) behind the back wall inside the freezer. If too much frost is built up the defrost cycle cannot melt it all. If the frost builds up enough to cause air not to flow properly you will not get enough cooling in the fresh food side of the refrigerator or most places in freezer. Since you saw a little frost on the visible part of the panel that would indicate there is a lot behind it.
To fix.... Remove the food and shelves from the freezer, take the panel off of the back wall and look at the coils. If they are frosted up, then use hot water and a hair dryer to melt the frost.
If the problem reoccurs then you may have something that has failed in the defrost system. There are 3 component to this system. The first is the heater, you will notice it on the bottom of the evaporator coils
, it sits horizontal and has two wires going to it. It can be tested with an ohm meter, it should read under 100 ohms. The second part is the thermostat, it is a small cylinder about the diameter of a quarter, it clips to the top of the evaporator and has two wires. It should have continuity when cold. If these two are working properly and the defrost cycle does not the problem would be the defrost control.
Let me know if you have more questions, I will be around.