Restarting your browser and load Google Docs in a fresh tab, and see if it still happens. We're investigating some causes of this that some people have reported. For now, if you're seeing "Updating" that's not going away while using Chrome, you can try in Firefox instead.
It doesn't work in firefox either. They still say "updating" and when I try to edit those it gives me the same error as in Chrome: "Selected field E7xtrv not returned from Docs backend"
That's an error from Google Docs, and it may help to just wait a little while before trying again. If this is a large document, you should also make sure you have "Automatically update citations" disabled in the plugin's Document Preferences window.
Beyond that, @adomasven would have to take a look. A Debug ID from Zotero for this happening may be helpful.
If you have existing citations that just say {Updating} and Zotero isn't actually processing your document (no progress window), then you will have to remove and reinsert those. There's a Chrome bug at the moment that is out of our control that causes this bug, the only workaround at the moment is to use Firefox.
Upgrade Storage
Beyond that, @adomasven would have to take a look. A Debug ID from Zotero for this happening may be helpful.