The issue here is that when the document was converted to a pdf, the system took its "best guess" at what text the heading should be as well as what those heading numbers should be. This issue comes up when you have mis-numbered headings or headings out of order.
For example, say in your document you used two headings; Heading 1 and Heading 3, in that order. Because there is no heading 2 in between them, these two are out of order.
To fix this issue, open the "Headings" > "Appropriate Nesting - Failed" in the issues list to expose the items here. You will need to:
- Right click on the first one and select "Show in Tags Panel". The tags panel will appear on the left and a box will appear around that text in the document.
- Now, you have to make a determination as to what this tag should be. Should it be a heading or not? If so, double click the tag and change the heading digit to be correct. For example, change "H3" to "H1" (these two values used as example only) if that corrects the order.
If the text should not be a heading at all, change "H3" to "P" (these two values used as example only).
- Go back to the accessibility panel, right click the option and select "Check Again".
- Repeat these steps until there are no more headings errors. Always start with the first one in the list.