Omen of Whittling

Ring had:
T4 rarity (still has) [ supposed target of omen]
T5 fire resist (was taken instead)

It's based off of the level in which the roll can spawn on the item, not the tier level of the roll.

Prefix rarity T4 is level 65
Suffix rarity T4 is level 63

Fire resist T5 is level 48

Meaning the omen of whittling would take the T5 fire resist in this instance