I do not know if any other quest is affected by this, but for me at least it's been like this these last two days:
Step 1: Get the "Dungeon Hopper" quest
Step 2: Go straight to kill the marked enemy type while the quest book says "Repeatable in X Hours"
Step 3: Open the quest book and see it didn't register the kill(s)
Step 4: Wait until the time has passed
Step 5: Go kill the enemies now and joy! Now the quest tracks the kills and is completable!
Apparently while the red text on the individual quest description says "Repeatable in X hours" (instead of when does it expire), in the quest log the "Expires" column for the quest says "No longer valid", which makes me think that there might be some kind of oversight there.
Hopefully this bug report will be detailed enough.
"Dungeon Hopper" quest won't register kills
Re: "Dungeon Hopper" quest won't register kills
Hi there - it isn't a bug at all, actually. 
Repeatable and expiration are different.
So, you can't register kills/collect/complete quest books if you're on repeat delay, or if your book is expired.
If you grab a quest book while you are on repeat delay, and your repeat delay isn't over until after the book has expired, then you'll have to delete the book and get a new one.
In the future when situations like this arise, just send us a page in-game
Repeatable and expiration are different.So, you can't register kills/collect/complete quest books if you're on repeat delay, or if your book is expired.
If you grab a quest book while you are on repeat delay, and your repeat delay isn't over until after the book has expired, then you'll have to delete the book and get a new one.
In the future when situations like this arise, just send us a page in-game
Re: I didn't understand how quests worked, nothing to see here.
Oh. Ohhhhh.
Now it makes sense.
So I guess if I got the quest again after waiting some time, the "repeatable" time would be lower?
Yeah, it makes sense. Ah well, things to learn about.
I was mostly a little confused because the only other quest I tried (the rat killing from the newbie dungeon) actually doesn't let you accept it until the time's passed, so it was somewhat confusing.
Sorry about that.
Now it makes sense.
So I guess if I got the quest again after waiting some time, the "repeatable" time would be lower?
Yeah, it makes sense. Ah well, things to learn about.
I was mostly a little confused because the only other quest I tried (the rat killing from the newbie dungeon) actually doesn't let you accept it until the time's passed, so it was somewhat confusing.
Sorry about that.