It's been a couple of days since this happened, so I can't remember for which location this was (I'd like to say Esior's Haven since I haven't gone very far into the story at all). But I received a quest from this location to retrieve 5 lost loot that the Nightfall bandits had stolen. I retrieved all five, then went to Explore -> Quest Log to clear the quest as I remembered doing for the other quests that I'd been clearing. However, the quest did not appear in the Quest Log. The only quest that was there (and still is since I've yet to clear it) is Level 20: Finding Saerielle (Faerina's Shrine in Umbra Forest).

I don't remember what the reward for this quest was or if I've already picked it up, but I'd like to say that I've yet to clear the quest.

EDIT: Nevermind. Switched to the Old Quest Log and found it there.