The ‘display as single group’ is a new feature of the basic online form builder. In the past when you create a pool of questions and published your form it would automatically, by default, be displayed continuously: each question or group at a time. This new feature allows you to display your basic form in one list of questions, in one group, on one page (with a scroll if needed).
Please note that this feature may not be used when you want to create a conditional form, because the flow of the form is dynamic and depends upon the form fillers answers and so the questions may not be displayed in advance.
In order to have the your form displayed in one group make sure that the ‘display in a single group’ checkbox in the ‘form settings’ is turned on.