To clear this up for everyone not yet experiencing this, I think it's about time to really start escalating this harder. It's not 'impossible' but it's nearly impossible thanks to an insta-kill mechanic that is laggy and extremely inconsistent.
A lot of guilds have been quiet on details due to shooting for world first, but at this point, we're all experiencing the same thing, admitting or not.
Video demonstrating the issue:
https://www.youtube.com/watch?v=sHo3AewOwog
Link to the bug thread:
http://forum.square-enix.com/ffxiv/t...mechanic/page2