I had a similar problem with a Kojin Beast tribe quest on 2/14. I was doing the one where you pick up debris. I though I had finished, as there were no more marks. I went on to do the fairy ones, when I saw I still had 1 of the 3 pieces of debris in my inventory. I returned, but there was no other pieces to collect, and the Kojin wouldn't acknowledge anything. I waited a day to see if things would reset, but they didn't. I filed a report. Started looking in my journal and found the quest. I clicked abandon and everything returned to normal.