Twin Cast Guiding Bolt

If I twin cast guiding bolt (as a child of the rift sorcerer) on Enemy A and Enemy B, and I happen to hit both, then (as expected) both have the active effect saying that the first attack against them will have advantage.

But then, if I attack Enemy A, I do attack with advantage, but the active effect is removed from both Enemy A and Enemy B -- I never got an advantage attack on Enemy B!