Storm Wheel can't be enhanced

Server: S1 Loralei

Player: Nessus

I got Storm Wheel as a prize for Wheel of Luck. I did an inherit from Apocalypse Wheel (+40). The result was StormWheel +20. I equipped it and tried to enhance it back up. Unfortunately, every time I try to do an enhance, it says "Breakthrough Not Yet Complete" but it's only giving me option to Enhance, not prompting me to do a Breakthrough.

Help!