Coould this be a permission issue, does the user that you use to look at the data have permissions to mange users with the Administrator role? If not the name might come up empty.
A quick check could be to have a look in the database directly and see if the data is present or not.
Aside from your probably security related issue as Erwin describes:
You shouldn't alter the AuditTrail module and should modify your Log_Webinar and Log_Account (duplicate??) to be the other way round, as a reference set. So the owner of the association is Webinar (or Account, but you will lose that data also in case of future update) In your current setup, when you upgrade the module in the future, you will lose this data.