You have to make sure you hit all of them within a specific time limit. What you'll notice is that, when one is activated, a green bar begins to fill around it. Once that is full, then it becomes inactive. So, it's imperative that you activate all of them before one becomes inactive. Missing one with a poorly timed button press will have the same result.
As you get further into the game, they become more difficult. There will be upwards of three or four in a row at times. But, upgrading that skill helps a lot. You can try auto dispelling if your skill is high enough, and it works a lot.
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