I had exactly the same problem with this instance (lost chieftain’s return). I tried 20 times, using different tactics, and discovered how to get through. Posters above are 100% correct- it’s all about the mobs hiding or being killed by npc’s. There are two major stall points- at the gates and inside the keep.
More specifically, to get all the way through the instance here are my tips:
1) Immediately tag ALL the mobs when protecting the settlers, defending the gates, and inside the keep. As a ranger, I ran around like made hitting tab and throwing axes and setting traps everywhere. Reset your buttons to all the traps you have for maximum effect. On my guardian I couldn’t do this, ended up re-rolling anyway and joined the Priory
(Not because of this bug, but because I had 3 norn already and wanted an Asura to balance things out a bit)
You have to tag quickly, the ogres kill the mobs quickly and tend to focus fire on one.
2) RIGHT after defending the refugees who fell, go up the hill BEHIND the Ogre Queen (forgot her name, totally swamped by her hawtness and can’t recall). There is a minotaur behind her, stuck IN the gate. She kills this one really fast, if she does you are sunk. Go tag it first, then go tag every other beasty or you have to start over.
3) Inside the keep, you have to run around in circles and tag everything. There is a scorpion type creature in the very back half-stuck behind a wall, and a few other beasties in corners. You have to tag all of them! I ran to the back, setting traps on the way, and tagged the back creatures then ran back to the front spamming TAB and chucking axes like I had stock in Axe Inc.
4) Where do all those axes come from? If you are not a ranger, hopefully you have a good aoe or bouncy skill for this one.
I hope that helps people. Until they smooth this one out, you CAN get through it with some frantic use of TAB.
Good luck out there,
-Gaurfang