The ability can miss if you are blinded. It can be dodged/avoided and it can be blocked(bubble/decoy etc). Avoiding the Haunt used to kill the Val'kyr but not anymore.
What I think you are referring to is that you try to haunt when the undead racial is active. IE you have been killed in the current turn or you are using Haunt on the final undead-racial turn.
This no longer works and is intended. Though it is not clear in the tooltip I guess. In effect you can only Haunt if you are "alive" and you have the possibility to ressurect when Haunt runs out.
Sadly there are a lot of nuances of certain abilities that are not very clear and there is no real good way of learning about them other than experience.
Not being able to cast Haunt while Undead racial is Active.
Why Flurry is not stopped after one hit against a Decoy/Bubble when pretty much all other similar attacks are.
Why many AoE(Thunderbolt, Arcane Storm) attacks now scale with opponents number of pets but some AoE(BONESTORM, Sunlight) do not.