This was going to be a bug report but I actually managed to fix it myself. If you are having trouble getting this achievement(i.e. the chest won’t open) try quitting the episode(not just the quest, the entire episode) and restarting it. The next time you do the Helping the Needy segment of Precious Aurene, you should see the eligibility icon for the achievement, which may have been absent before. Now you should be able to open the chest before completing the quest as normal.