I did two full runs where we have defeated Giant Tengu but I did not get any kill credit for defeating Giant Tengu. Do we have to last hit the boss in order to get credit? (I was a knight and actively attacking the boss, along with an Acrobat).
#Bird Assassins (2) (Defeat Giant Tengu)
vast nexus
placid ember
This is not a bug. Be aware that not everyone has same quests. The Giant Tengu must be killed by player with this quest.
lucid silo
more precisely, the lasthit one the monster must be by someone who has the quest, then the objective is given to all in the party with the quest. But like ppap said, if your acro only has the first 3 and not the giant tengu quest and lasthits it, it is not awarded to anybody even if they have the quest