Square Enix has warned Final Fantasy XVI players that it's aware of a potentially progress-impeding bug, specifically affecting players trying to boot up a New Game+ run. The good news is that the developer is prioritising a fix and will push out a patch once a resolution is found.
On Twitter, Square Enix apologised for the inconvenience and offered advice on what to try. The issue is when players select to start New Game+ and skip the prologue; there is a slight chance that needed party members won't appear, making progressing through the main scenario quest, "A Chance Encounter", impossible.
If you are affected and the patch hasn't arrived, Square Enix recommends loading the saved data created immediately before firing up New Game+. Then, travel to a new location on the world map, save the game, and use this data when launching New Game+.