The idea is that you cannot jump to a scene you've been to before, so after you've visited all scenes the button won't have anywhere to go!
If you want the start button to reset the cycle, you'll need to restore the sceneNamesForJumping array. This is currently set in the Head HTML
<script> tag, but could instead be placed as an on scene load action in your first scene.
var sceneNamesForJumping = ["p1", "p2", "p3", "p4", "p5"];