I was at the Red Dragon Event, was there from the beginning, got the quest, didnt die once, and had Sjinderson tagged the whole time. I did not recieve credit for it. SS included. I shouted to Sjinderson and he didn't respond.
Not getting quest completion happens for a few reasons.
1. You were dead on my death.
2. You were dc'd on my death.
3. You were not within range of me on my death.
As the screenshot does show the right quest the other possibilities are mute. However the screenshot does not actually prove participation in the event as it is from a minute after my death. No damage log or you attacking.