Hi,
It appears that if one member of a party starts a group dungeon event before the others are present, the opportunity to take the quest is lost. This can result in some of the group not having the quest, thus receiving no recognition for quest completion (xp, skill point, dungeon completion on map) despite finishing the dungeon with the group, while those that did get the quest receive full completion.
To avoid this from happening please allow all group members to individually pick up the quest at the dungeon's commencement.
Thanks,
A