I created this document for a client more than a year ago, and he just now noticed a really odd bug in the last PDF rendered. Every chapter, starting with chapter 4, is being recognized as the first chapter. Previous PDF exports show all chapter numbers rendering correctly, but unfortunately I long ago overwrote the previous versions of the InDesign document. The attached screenshots should demonstrate the issue. The only changes made from the previous version to the new version were corrections to the text itself—minor punctuation issues, typographical errors, etc.—so I see no reason why this issue should be happening from one version to the next. Googling has so far gotten me nowhere. Does anyone have any idea what's going wrong?
Try to select all chapters on the book panel and from flyout arrow select update numbering>update all numbers, then from book page panel click on synchronize button.
Did you set the chapter numbers for each chapter in the numbering and section options in each doc? That's where that variable pulls the number, I believe.