Zotero cloud syncs only some PDFs

Hi,

I am using a BOOX NoteAir3C, v3.5.4. When using Zotero through the BOOX cloud sync, I can log in and my library appears to load normally. All folders and metadata are there. However, if I want to access a PDF, many are absent under the 'attachments' tab of an entry.

The pattern is, PDFs that are manually added to notes are available, but PDFs that are downloaded automatically though Zotero are not. These PDFs are available on all my other devices and through the Zotero web library.

This issue seems very similar to what is described here:

https://forums.zotero.org/discussion/116034/zotero-cloud-document-sync-integrated-into-boox-library-app

Has anyone come across this and found a way around it?