As reported by forum user BRUCE, the ESV audiobook ("David Cochran Heath") stops playing at the beginning of new chapters and the computerized macOS (or windows) takes over. I have no idea if this is related, but am wondering if it is related to the new smaller "Bible Indexing" command.
EDIT: I haven't had a chance to confirm, but it may be specific to certain books. My test case was between 1 John 1 & 2. See OP for more.