So as far as I can tell, NIN LB now works like this with the new snapshot:

1) You hit NIN LB button on target
2) At that moment, if the target is below 50%, they will die (later on when animation actually finishes, though)
3) NIN LB animation goes off, target can still guard, heal, move, etc
4) NIN LB animation finishes, target dies

I'm not sure what the purpose of the new snapshotting giving people time to react if reacting doesn't do anything in the end? Either revert it back to the old way so you just are locked out of moving/actions ASAP, or allow our healing in the NIN LB animation window in order to have a chance to avoid the instant death.