I thought this was going to be about the numerous amount of bugs that he has if you DPS too fast. With all of your group 4 levels higher, that may have been the problem. Did you suffer from:
- continously spawning adds instead of spawning on emotes?
- non-clickable plates, causing him to receive his buff and the central column to not raise so he could be damaged?
- him getting his buff and sniping for 75% of the fight even though the plates were clicked and the column raised back up?
There was one or two more, but I have forgotten now.
Getting stuck in the middle (and then crushed) was another one. Sometimes, if you're meleeing HK-47 in the middle, and he's about to do his shield call down (a red circle appears around him) the game bugs and you can't run away, like there's an invisible wall. This is definitely the buggiest fight in the game that I've encountered!
Still, I find HK himself not that tough. Most wipes IME seem to happen because the additional droids ambush the rest of the party (especially the healer). Basically it's this:
- The tank has to keep HK's aggro, but not necessarily always attack him. Instead, the tank should also tank the new droids.
- Kill the adds first. When they're about to appear, get ready to monster them as soon as they step out of their niche. Even better, if you have an unlimited droid CC (like on a Sentinel), have a plan. Say "we'll CC the left one, so everybody focus on the right one first".
- Whenever the shield is about to come down, quickly position yourself at the four corners of the shield to immediately bring it back up.