Integrated PDF reader doesn't allow sorting by headlines (document structure) anymore

[CyCosmic]

Hi,
recently I noticed that when opening a PDF in the integrated PDF Reader there are a couple options missing on the sidebar.
I have a really big PDF from my cars wiring diagramms that I was always able to go through the headlines of by using the "document structure" in the sidebar. 
With the rework of the sidebars design this feature is now greyed out in the new Version.
What is the reasoning for this and is it something I can fix myself?

[marco]

@CyCosmic this looks like an unintended regression, the document structure should still be available in the new UI (click the button on the top left of the PDF UI, then the dropdown right below that at the top left of the pages panel). Could you share the PDF if you still don't find the document structure?