Has anyone seen Excel workbooks become corrupt after using M365 Copilot to summarize data?

Hi, I would preserve both affected files before testing further. If they are in SharePoint or OneDrive, restore a previous version and compare the workbook structure, size, external links, macros, data model, and coauthoring state. Update Office, then try Excel's Open and Repair on a copy. Reproduce only with a sanitized workbook and version history enabled. Collect the Office build, Copilot interaction time, file location, and any Excel event or diagnostic logs, then open a Microsoft 365 support case. Until the cause is known, have users work on copies of important workbooks before asking Copilot to analyze them.