The issue is opening your document in Google Docs. The Google Docs editor doesn't support the features that the Zotero Word/LibreOffice plugins use to store citation data, and any stored data will be discarded if you open the document in Google Docs, leaving only the plain text. If you download the document directly from Google Drive by right-clicking and choosing download or sync files using Google's sync program, you might be able to store documents in Google Drive without losing your connection to Zotero. However, I'd generally recommend avoiding the issue by using a cloud provider that doesn't break Zotero functions if you use their built-in editor, such as Dropbox or Microsoft OneDrive.

For your current document, try to locate a previous version of the document from before you opened it in Google Docs, such as by right-clicking in the Google Drive window and downloading it directly from their, looking at the Previous Versions that are available to restore in Google Drive, or a version of the file stored elsewhere.

(Feel free to keep responding in French.)