Document label mismatches happen when users create, upload, or update Office documents in SharePoint sites and give the documents a higher-priority sensitivity label than the one assigned to the site. When this happens, SharePoint Online creates a DocumentSensitivityMismatchDetected audit event. Unhappily, that event doesn’t tell us who caused the mismatch, but some work with PowerShell reveals all.
https://office365itpros.com/2022/08/23/document-label-mismatch-audit/
