Dead party members keeping claim on monsters
This is rampant on my server I don't know about others but basically if a party member claims a mob, dies and keeps that mob targeted while dead it will stay red to the dead guys party and not turn yellow but it will act like it is passive. So what people are doing at NMs is attacking it as soon as it pops, dieing and keeping the claim with themselves dead while the rest of their group gathers up to kill it. While being glitched like this the monster can still aggro other people but they will be unable to claim it or use actions against it.