Thank you for the advice. We'll give it another shot with the tactics you describe.

Tried to complete the HK-47 fight on hard mode in the False Emperor flashpoint tonight. HK-47 consistently killed his target after his vanish phase. We grouped up. We did AOE to knock him out of stealth. We cast cleanse on his intended victim before they died. We cast heals on his victim before they died. We were unable to prevent the death. ... the things we'll try next time are: (a) just AOE harder and longer during his stealth phase (b) have the intended victim run away © spam heal the intended victim I don't think the fight is working as intended, which is why I'm reporting it as a bug. Hopefully this post helps someone else out. If anyone knows what we're doing wrong, I'd love to hear it. Thanks.