Missing indents in cross-reference selection

I am using Libre Office I am working on a document that I have been working of for literally years using Libre Office. What I am finding is that when I wish to add a cross reference by heading, the “Selection” list is not indented. The easiest way to describe this is by an example:

If we look at the selection list on the right, some of these are heading 1, some heading 2 and some heading 3. When I create a brand new document, and create heading and then look at the selection list, I see the heading nested within each other which aids my ability to find the heading I am looking for.

Does anyone know what I might have changed or corrupted such that I have lost the indentation of the headings?