Literally every time i've done this quest, it has bugged out. It's impossible to pick up all 3 rings. the only solution that i 100% know for a fact works to fix it, is to get the first 2 rings, then invite someone else to the group and have them pick it up for you. Oh, and than that person is unable to get all 3 rings. Either way someone draws the short straw. I've also heard that doing it solo can fix it, but i haven't been that in person, so i'm not sure.