Issue

The following warnings appear in the backup:

Failed to resolve personal site owner. A user may not have a valid Microsoft Office 365 license with a SharePoint plan enabled.

Cause

A user account has been deleted, but their SharePoint personal site was not

Resolution

Delete the orphaned site as follows:

1. Confirm the account has been deleted
2. Open an administrative Powershell
3. Download/Install SharePoint Online Management Shell: Install-Module -Name Microsoft.Online.SharePoint.PowerShell
4. Connect to your Tenant and login as global admin: Connect-SPOService -Url “https://{companyname}-admin.sharepoint.com”
5. Delete the ophaned site: Remove-SPOSite -Identity https://{companyname}-admin.sharepoint.com/{url}/{sitename}

“The requested operation is not supported for site”

If you see this warning in PowerShell, the site is being held by a retention policy and can’t be deleted. See this article on how to exclude from retention, then try the command again