Turns out the issue was with the Numbering setting for paragraphs, set
at the book level. It had been set to Continue paragraph numbering,
which meant the numbered list in the LOP format continued from the
previous LOP. Setting the Numbering to Restart paragraph numbering
fixed the issue.
The first thing I check when that happens to me is whether I have a
conflict between the numbering for the file as a standalone document and
the numbering for the file as part of the book.
The first is Format > Document > Numbering when inside the document.
The second is accessed by
