Cold fridge, warm freezer
I had pretty much the same problem with an old (I think) Frigidaire. It had the compressor &amp; evaporator in the bottom of the fridge and used a rectangular air duct to get cold air up to the freezer.  After a series of very humid days and lots of ice use (opening and closing the freezer door repeatedly) the air duct iced up.  I had to use a hair dryer to blow hot air down the duct to defrost it, emptying the drip pan under the fridge each time it filled up.