Welcome to the forum.

In this case, the attachment really porovides us with no clues.

How EXACTLY is each of you accessing the file? Via a browser? Via the desktop? When you say OneDrive, do you in fact mean SharePoint? Is this over a network?

It is these details that will be relevant, not the contents of the workbook, unless you are saying that you are able to co-author other workbooks, but not this one.

More details, please!