I've got an articles with 3 pages. On the right menu it says article index, then 1-with article title
and 2- and 3- are empty. I can't find where to add to the index.
You have to give all article pages page titles.
You can do so by entering this page break code:
[pagebreak=Your 2nd page title here]
assuming pagebreak is the page break delimiter in your settings.
The first article page automatically takes the title as the page title.
You need to add this info to the upgrade's .txt file man. :)