The QR scanner could return the user back to the game page if a camera is not found (after the OK button on the alert has been pressed).
It is not very clear which value represents the points in your leaderboard (although it is in bold). Your leaderboard could use a better design, if there is time.
A loader is typically aligned in the center of a page (yours is currently at the left).
When returning to a previously started treasure hunt, you could add an option to start over.
When the restart button is clicked the progress of the treasure hunt is lost. You should display a confirm dialog before this happens.