For a long time now, the game has had an issue with obtaining credit for killing enemies when in very large groups, a problem that became worse with the addition of the Megaserver and scheduled world bosses that come with it. Even so, this bug is not limited to just such events, it can also happen in World vs. World, in Dry Top sandstorms, and any other place where large numbers of players gather and fight the same things.
The problem is that only a limited number of players are capable of receiving experience and loot from each given enemy. The exact number of players, I can’t say, but the limit seems to be around 50, enough to be problematic given that the maximum zone population in most places is 150.
After testing on world boss events, I’ve determined that the trigger that determines which players get loot and which players do not is not tied to damage at all, but rather to speed. The first players to hit a given enemy will be flagged to be able to receive loot from it. Once the maximum number of loot-receiving players has been reached, subsequent players to hit the enemy cannot receive loot or experience from it no matter how much damage they do. The only recourse a late-coming player has to obtain loot is via party mechanics. If the late player is in a group with someone who hit the enemy in time, the loot credit will be shared within the group.
This bug is easy to reproduce in any situation where there are large numbers of players. If you hit an enemy quickly once it appears/becomes vulnerable, you will obtain loot even if you do poor DPS to it. If you are slow in hitting an enemy and are not among the first 50-ish players to do so, you will not obtain loot even if you do tremendous DPS to it. This causes other issues due to the lack of kill credit received. Using the Legendary Karka Queen as an example, it’s a heavily-zerged world boss that, with its Karka Roll attack, is capable of downing players who aren’t aware enough to dodge. If you fight the Legendary Karka Queen and its first health bar is depleted soon after it does a Karka Roll, you’ll be able to see who was slow to hit it among the 100+ players present. The downed players who had hit it soon enough to receive loot/XP will rally when the first health bar is depleted. The downed players who were too late and will not receive any loot or XP from the Karka Queen on its death will not rally, due to the lack of credit, and will remain downed from the Karka Roll.
This loot bug leads to the risk of antisocial behaviour appearing. Using the Great Jungle Wurm in Caledon Forest as an example, there are three pre-events that must be cleared before the “Defeat the Avatars of Blight” event starts. The problem is that players who go and complete those pre-events wind up being too far away to return in time to hit the first Avatar of Blight that the mass of players waiting will jump on, thus causing them to miss out on an Heirloom Seed Pouch (possibly two depending on how fast things go) because they went and did a necessary event to progress the world boss sequence. Similarly, players who go to the “Close the Mist Portals” pre-event in the Frozen Maw event chain wind up being too far away to quickly hit the Champion Svanir Shaman, and thus cannot get the Icy Strongbox he drops on his corpse unless there are either very few players present (unlikely in a Megaserver) or they are partied with someone else who stayed behind to hit the Shaman quickly once he becomes vulnerable. Players should not be punished for completing events, but that is the case in these situations.
This bug goes pretty deep under the hood of the Guild Wars 2 engine, I imagine. It has existed since the start of the game, but even now remains largely unknown, with only the few players who have noticed the strange occasional lacks of loot and have decided to put in time and effort testing that out being able to figure out what exactly causes it, with most people affected by the bug thinking it was their own fault for “not doing enough DPS”. It would certainly be good to hear from a red name on this issue, to see if they’re aware of it and if it’s something that’s feasible to fix. I do worry that the longer it goes unfixed, and the more people who learn the truth of how loot is assigned, the worse certain events will get, with races to try to tag champion enemies being set up and harsh words being tossed around once some people inevitably are left out in the cold without loot.
One of the big selling points of Guild Wars 2 is that you should never be annoyed to see another player present. As things stand, when you see seventy-five (or more) other players present, you know that some of them are going to be slow and thus receive less rewards as a result.