Even if it does have more bosses, the thing is that it says it's done. If it doesn't require all the bosses that really should be noted somewhere. I don't see how I should be able to get the individual dungeon achievement without also getting the bundle achievement. If they're decoupled that really seems like a poor design choice. That being said, this problem is not pervasive. This is the only character on which I'm having this problem. Others have the achievement complete so it's a nuisance at best. Still shouldn't be that way though.

I doubt highly that this is the problem. All six of those bosses are dumped neatly on your path from start to finish. There's no way I haven't killed those. It would actually be extremely difficult to avoid them even if you wanted to, save for maybe Ganakton. Like Fanged Menace, he's right in the way. You'd have to go to very great lengths to avoid that room, if it's possible at all. Ganakton might be missable though the achievement lists him as done anyway so that's confirmed. Sliklenia you must encounter to turn the switch, and she's also listed done. Ixniaa is standing on the other side of the bridge and auto-aggros once you cross it -- unavoidable. Ancient Lurcher you must pass to get to the final tunnel, pinned down by those wizards. Then the last boss obviously is unavoidable too. I almost want to try to miss a boss now just to see if it's even possible.

Maybe you didn't but it never hurts to check...

@ZOS_GinaBruno I'm afraid not. I can't even replicate the problem on another character. Other characters have completed this without a hitch. This one character is having this specific issue. The screenshot says the entirety of the story really. I don't know how to proceed with this.

Even some next steps or something would be appreciated... flying blind here.