We use the bibtex export via the Zotero API and save the bibtex into our database. The @incollection seems to be changed because in the current version there is booktitle for a book section is missing. We still have unchanged references in our bibtex that shows that the book title was exported correctly at the beginning of last year.

Did something change in the Zotero export to bibtex? Do we have to change something in our settings or is it a Zotero problem?

I also tested the export in the Web Zotero and also there the book title is missing for Book section while my stand-alone Zotero still exports the same book section correctly with the booktitle shown in the @incollection.