I have the same experience. The reaction triggers BEFORE the hit, which is wrong. Also, for AOE spells, it should tell you which creatures you rolled a hit on before confirming to use the ability!
No competent DM would force you to waste the scarce channel divinity abilities on non-hits.
Larian, please fix this!
Chris
Edit: In the D&D rules (and in the ability description in game) it says:
Channel Divinity: Destructive Wrath
Starting at 2nd level, you can use your Channel Divinity to wield the power of the storm with unchecked ferocity.
When you roll lightning or thunder damage, you can use your Channel Divinity to deal maximum damage, instead of rolling.
and not "Before you roll to hit...".