Hello There,
Mobile icon in the vertical bar along with the save buttons;
Once you click it, it will display different screen sizes on top:
You can toggle the screen sizes and you will see all the sections being hidden/shown only to that specific screen size.
You can simply delete it by clicking the section and find the delete button.
To make sure that the section is display in all screen sizes, please click each section to inspect if it is hidden based on screen size width.
Hope this helps.