I ran into this issue earlier this week with one book, and I have suddenly seen it happen with another.
We moved from Frame 10 (where all worked fine) to Frame 12. Run an update of the doc, and for some reason, the auto-numbers in the TOC seem to assume that each chapter is only a single page or two pages long. But when you open the chapters they are longer than that. Within the chapter numbering seems to continue fine, until you open the next chapter and it says it's one page beyond the first page of the last chapter. What up, Framemaker? Nothing has changed at the chapter level in these files from when I last ran an update in Frame 10.
Anyone else seeing this issue?