This is just a weird error I have and I've noticed lots of other people have too. When you go to my profile, you look down at the "Exploration Info" (or whatever it's called) box in the bottom right corner. There is the Gold earned, scales earned, and that sruff. But if you go down past that there is "Dungeons cleared, Bosses defeated, Elites defeated, and Superiors defeated." Well, this is what I've seen for many people, even all the way up to 70:

Dungeons Cleared: 0
Bosses Defeated: 0
Elites Defeated: 0
Superiors Defeated: 0

But I know I have defeated several bosses and I am pretty sure I have cleared the Nightfall Bandit Dungeon. Why don't those thing show up, though?

Largely all of those types of stats on profiles pages have been broken or removed or discontinued by now. Battles won/lost is pretty much the only stat accurately kept track of.

Someday we'll bring all of this stuff back with much better tracking systems and whatnot. But at the present time, it's just not really feasible to keep track of them.