How do I fix a text box that displays correctly in edited and slide preview, but incorrectly when I access the slide during the full file preview?

Remove or deactive the 'Submit unassigned' trigger on Button1 and check again.
Make a habit of naming Buttons. Button 1...says nothing... when you change that to 'Submit Button' its clear in the trigger window what button it is. Not that that causes the issue, but its a good habit to learn and use... Name everything so its clear what it is. Storyline tends to create useless names by default.

If thats not fixing it...share your sample