Test User Migration 1

I am currently in a dilemma with my custom calculated attribute as it is giving an incorrect result. Could you please help me with this? It is giving me "Achieved SLA" even though the result should be "Not Achieved SLA".

IF ((([Ticket type]="Incident" AND [Ticket priority]="High" AND SUM(% Achieved SLA tickets)<99.5))) THEN "Not Achieved SLA"
else "Achieved SLA"
ENDIF