Refrigerator temperature fluctuating, some ice build up

[JohnnyH]

Our KitchenAid KBFS25EVMS00 French door refrigerator starting having issues recently.  The freezer has been consistently cold, but one day the refrigerator temperature rose to about 60.  No sound from the evaporator motor.  Next day temperature is fridge was back in the 30s and I could hear the evaporator motor running, then next day temperature rising again.  We investigated by removing the freezer shelves, ice maker, and rear panel of freezer.  We found the copper coil encased in a block of ice, including the defrost thermostat.  We melted all the ice away, put everything back, and for two days now it's worked fine.  Now wondering if we'll have the same trouble again, if the ice will build up again due to a faulty part.  Or if this issue was due to slow ice build up when a door might have been left ajar.