Challenge
Backup jobs with SharePoint Online or OneDrive for Business items fail with the following warning: "Processing OneDrive Username (https://orgname-my.sharepoint.com/personal/user_name) finished with warning: Failed to backup item: /personal/user_name/Documents/File.zip, The remote server returned an error: (400) Bad Request".
Cause
Items being backed-up might be blocked by the internal SharePoint Online antivirus. For more information, see this Microsoft article.
Solution
To check whether items are infected, open OneDrive or Site which cannot be backed-up and try to download files manually. If the files you are trying to download are infected, the following error appears.