At first we thought that maybe this is a feature on the hardest difficulty but after having two players downed by the same Wolf Spider, over 100cm apart, and I was running back and forth between the two picking them up, which caused the constant re-aggro over and over and over again... I was like.... Yeah this is a bug. I did email the support team and they did confirm that this is not a feature so hopefully they can have this fixed in a micro patch fairly soon.