A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
That was most likely because Microsoft 365 by default saves your documents to OneDrive online, if you experience the problem again with any Office documents, try downloading them from OneDrive online to your PC, or if OneDrive is set to 'Files on Demand' disable that in OneDrive settings so a copy of your files is kept on your PC drive.