I've had this quest for a very long time (took a 7 month break).
I can't finish it. I have long killed the required mobs, but when I donate the coffers (have many), they do not count.
It seems to always be in Tiamat Reclamation mode in the Well of Dragons. Been trying for 2 weeks.
I have a friend and they have the same problem. So when can you turn these things in and finish the quest?