Administrator Assigned Agent as Docked Filter for existing report: What table and how to?

Summary:I added to a column after I have join the tables in a report and in a type column I added as filter: first(accounts.display_name, transactions.created). I also added docked filter with the following joining the tables with type_4= Assigned or Created = transactions.trans_type , and I'm not getting consistent results. Created provides more consistent results but not perfect. It skips and provides the final assigned when the agents are few reassigned in the audit log. I don't understand why is happening?

What are my options for this? I want the very first agent the incident was assigned by administrator.