Might be related to AOD-6510. I can't embed a Google spreadsheet into my Confluence document. I get the same 404 error as quoted in AOD-6510:

An error occurred while fetching the document. Please check to make sure that the document ID is valid and tat the document has not been deleted.

Interestingly, it found the spreadsheet and let me select it. It just doesn't show. I changed the sharing on the doc to everyone in my organization.

When I paste the link in the error directly into a browser I get a 404.

Attached screenshots of the issue.

Oh, also I can click on the "edit" link at the bottom of the page (see screenshot) and it takes me directly to the Google doc in edit mode.