Did you place hot food in the freezer?
Reason
When hot food is placed in the freezer, water vapor created by the food can
stick to the product surface to form frost or icicles.
Sudden formation of icicles on the freezer ceiling mostly occurs when the door is not tightly closed.
How to fix
Cool hot food first before placing it in the refrigerator.
Clean the icicles on the ceiling with warm wet cloth.