just occurred to me we might be referring to different bosses
potentially for clarification, are you talking about dermapteran Swarm Queen Ravna and the Act 3 Quest ? (Culling the Swarm)
or are you referring to a bounty?
involving either Ravna,
or one of the Bee/Wasps; Ronaprax, the Grand Queen/Ulraprax, the Hive Matriarch?? (Bounty: Hive Royalty - Official Grim Dawn Wiki)
because if you’re are talking about a Bounty, then it’s totally normal behaviour that you can’t kill your target before you have the bounty objective in quest log