This can happen if;
1. Inner fan has failed will cause ice to build up rapidly
2. High humidity in the air can cause excess ice and more water in self evaporating drip tray to dispurse
3. Could have small gas leak, this may show a lot of ice at one corner of the cold plate in fridge

New fan part number is HUS-SC23-FAN, cost is $49.00, email details below.