Server Version#:1.19.5.3112
Player Version#: 220.11 (Prologue)
There seems to be a problem in detecting chapters for multi-volume works.
For example, if you have a book titled “The Four Gospels,” and there are four files in this book (Matthew, Mark, Luke, John), and each has corresponding chapter markers in the m4b file, Plex will sometimes show all the chapters of the individual files, and other times it will only show the four files/book as chapters, and no internal file chapters.