In the process of killing the adds prior to the Hagara encounter, all the adds spawned at the same time making it extremely difficult to kill them all. Once one group of adds would be killed they would simpy just respawn. Eventually Hagara herself came down along with all the adds that spawn on the platform. Even after exiting the raid and performing the reset all the adds were still present and even when taking the time to kill one pack at a time they simply just respawn.