This is happening because the spinner that displays the vacancies has not been set up correctly.
To resolve this, follow the below steps:
Select Content, this is normally found in the Configuration or Admin menu.
Click Pages and then select Recruitment Pages.
Click Vacancy Content Page.
Click on Edit to the right of the screen.
This will open up a new dialog window that will allow you to edit the spinner.
Click on the Spinner that needs editing
This will open up a new dialog showing the spinner settings.
Populate Display Type, No of Vacancies in Spinner and Sort By.