Most likely, you used Strength of the Waking Island before Absorb Essence. When you use Strength of the Waking Island, it checks how many absorbed Presence each Spirit has, and sets up the number of repeats available at that time. So if you want to get another repeat, be sure to use Absorb Essence first!

You can see the number of repeats each absorbed Spirit has available by looking at Serpent's full Spirit panel. Each repeat available is indicated by an icon on their absorbed Presence.

Alternatively, you may be using a Spirit-targeting Power, or an Innate Power. Strength of the Waking Island only allows you to repeat land-targeting Power Cards. Plus, you and Serpent have to have enough Energy between you in order to pay for the repeat.