Possibly on the last event make sure the value is an integer with int(LocalStorage.ItemValue)? Not quite sure... I imagine it IS getting something, otherwise the high score would remain at 0.
Or does it have the same problem with all the localstorage events disabled as well?
Edit: I don't see where you set the HighScoreText to HighScore anywhere... Maybe you're just not displaying the number? When you check in debug mode, does the highScore variable show the correct number? Reference capx: