This boss doesn’t resets properly after a wipe, the Spider Hatchlings and Undergrowth Recluse mobs don’t despawn after the boss goes out of combat.
This means that on on the next attempt you’ll have to deal with whatever spiders you got left from the previous attempt, this translates in 50 mobs spraying poison at you right from the start which is obviously a bug. Please fix this on 6th aug patch.