Disable Report obfuscation

Make sure that the Report setting for de-identifying users user, groups and sites names is disabled in your tenant:

https://docs.microsoft.com/en-us/microsoft-365/admin/activity-reports/activity-reports?view=o365-worldwide#show-user-details-in-the-reports

If you leave this enabled, OfficeExpert will be unable to map user data with activity data.