Don't believe random dungeon on it's own levels up Undaunted. You need to do the pledges, Bolgrul dailies, get dungeon achievements and complete dungeon quests. So, if you aren't in that specific random dungeon for first time and doing it's quest, or get any achievement while there, your Undaunted level won't change.
You only get undaunted xp a few ways.
1, the first time you complete dungeon and trial related achievements.
2, undaunted quests, the daily dungeon pledge with more xp given if you complete hardmode and the daily delve quest.