It has occurred to many people, including myself, and after gathering some information from the people who hadn’t gotten the chest, this problem has always occurred due not actually ‘participating’ in the event. In order to get the full reward, if you are a Conditioner you also have to help clear out the Veteran mobs, tag them and the boss itself to register in the event.
This problem often occurs to Conditioners and Deboofers for the reason explained above, and ever since I made sure that during the first phase of the event I was contributing to the killing of Veteran Wurms while waiting to synchronise the decapitation of all the 3 heads, I have always gotten all the rewards I was supposed to get.
I am not stating this is how it is supposed to work, but perhaps it is, and while you wait for an official answer from the ArenaNet team, I thought I’d share how I solved my problem. Try it out
