I'm having a similar problem.
In the first act, no boss in the first dungeon.
Went on to the second dungeon, again no boss.
You'd expect at least one boss to be in the third then, right? Well, none.
I did of course proceed as far down as I could in them. I had to leave act one without having been able to complete any of the BF quests.
Can the BF's be so random that sometimes there just are no bosses? Or is this a glitch?
Any thoughts?