Describe the problem. Be as specific as possible!:
Upon completing the 6th day of the Artifact Hunt, Gaga gives you two options to choose as prizes. Choosing either option closes the dialogue window as if pressing "End Chat". The quest is not completed and there is no dialogue in the chat box indicating something is wrong.
You can try all you like, the Star for the quest never goes away. Going up to Gaga to try to claim the prize also does nothing. Tested with 4 Equip slots and 3 Use slots open.
Edit: I just read that this prize is (seems to be?) the permanent prize for the 8th day or participation in the Artifact Hunt. Will update tomorrow to see if the 7th day is attainable without being able to complete the 6th.
Edit 2: Just like a previous event quest, you are allowed to continue and do the quest for the 7th and presumably 8th day. However you are not allowed to claim the prize for the 7th day until you claim the 6th day, which as mentioned is impossible. Last test is maybe the ability to claim the 6th day prize upon completion of the 8th day quest since that seems to be the quest.
Images of problem