I was doing the weekly sundial bounty that required 300 scorn kills. Loaded into the dreaming city to do the bay of drowned wishes lost sector. While killing many screeb I noticed that none of them counted as scorn kills. Not an issue of chain explosions not counting because even the one that I killed by shooting it didn't count towards the bounty.
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The normal scorn in the lost sector should count towards the bounty, Screebs are almost like taken thrall in the sense that they are so easy to kill that in some cases they don't count towards bounty completion, weapon kills, or quest steps.