[DNSB]

If you match a book on the device manually to a book in the calibre library, does it stay matched? I'm wondering if the multiple titles being the same are causing the issue. I haven't noted that issue on a Kobo but then I would use Attack on Titan Vol. 06 as the book title and then repeat the title as the series name and the volume number as the series index.

There might also be an issue with how the actual file name on your Boox is being created. Do you have a save template set in the Boox driver?

Bounce a query off my daughter and she has read some of the series and uses Hajime Isayama as the author.

Edit: added image from one book series I have with the identical titles.