I have a quest called "Hero of the Nopon" in which I am challenged to a series of burglary competitions. I am called upon to steal Mor Ardain emperor Niall's underwear mid-quest. I go to the entrance of Hardhaigh Palace but all I see is my competitor thief standing outside with a bunch of guards. I can't talk to him. There is no indication on the map of where to go to advance the quest. What do I need to do to complete this part of the quest?
I'm doing that quest now, I believe that you need to have all prerequisite party members available and/or active. From looking at the quest details, you need to have [Nia, Tora, Morag, Zeke, Pyra (I had mythra version and it still worked) and Boreas]. As long as you have the main characters listed available (you have the option to put them in your party), Mythra/Pyra & Boreas as active blades.
Hope that helps!