InDesign Book keeps saving duplicate files

My team uses InDesign books all the time so multiple people can work on a project simultaneously. Books are supposed to only allow one person to open each file within the book. If someone already has a file open, the book is supposed to show a lock icon next to that file and no one else can open it.

However, this week, InDesign has stopped doing this. It allows us to open a file in the book even if someone already has that file open. Instead of making the file read-only like the few previous times we've had this problem, InDesign allows both people to edit and save their changes, and makes a new duplicate file when saving the second person's edits.

This is a very frustrating problem, because we now have to check ourselves if someone else has each file open - which InDesign is supposed to do and has always done before - and manually re-merge duplicate files. At one point a file in our most recent book had FOUR duplicates because of this bug!

Does anyone else have this issue and has found a fix? InDesign 2024, version 19.5 - it looks like this issue started after that update so maybe there's a bug in it that caused this? The image shows a file from our most recent book and the duplicate created by InDesign.