Keep in mind you have to go all the way to the end of the dungeon before the diner scene triggers. You have to see that the monsters aren't there before you can bait them with the salted char. Sakuya > Dungeon > Blaise > Boss
You also can't be in the middle of a request, possibly for any of those things. If you're going to the board and picking up a request you think you can do while you're roaming around it'll prevent story scenes from happening.