Replacement Variable

I'm using workbench 5 and my current query looks like 


SELECT Unique_ID, Incident_Date, Incident_Time, Incident_Description

FROM Incidents

WHERE Unique_ID > !{lastvalue:Unique_ID}!



In my replacement variables, I have the column set as "Unique_ID"  and the value as "!{lastvalue:Unique_ID}!

I've run this query using both the append and the replace update method and everytime it gets stuck returning the message "Replacing Last Value query at position 146" 3 - 5 times a second, sometimes freezing workbench altogether. What am I doing wrong? How do I get the job to run successfully and update the value in my replacement variable?  


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