Issue
When editing a form, a field called 'x' is visible. However, when previewing the form, the field is not visible.
Solution
The reason why the field 'x' in the form edit mode was not visible when previewing the form because the form that was being previewed was the approved version which did not contain the field 'x'. The field 'x' was in the draft version of the form, which needed to be approved in order to see it in the preview of the approved version of the form.