Plot hole: All through the movie it is made known they have to get through TeKa to get to TaFiti. They fail and Maui leaves. Moana goes back alone and makes it through the barrier island and Maui returns to help her. The problem is he returns from the direction of TeFiti, if he can do that He could have done it all along, and therefore discovered TeFiti was gone.
Plot hole: Not knowing the twist at the end, Moana should have been overtaken by hopelessly knowing that Maui and a functioning fishhook are required to return the heart. We see right at the beginning that Maui was only able to reach the heart's resting place by transforming into a small lizard. The whole triumphant song is completely undermined as, based on available information she has 0% chance of success.