Assassins Strike can fail

[DarknessEternal]

The combat log will show a successful hit roll. Power goes on cool down and endurance is lost. No damage occurs.

[Solarverse]

This usually happens when either A: Your target goes out of LoS or B: The collision mechanics causes you to get pushed in the middle of an Assassin Strike late enough in to your attack that it does not interrupt it, but instead robs you of your hit.

 

The first one is normal and is working as intended. The second one is a flawed bugged with the Collision Mechanics that I have brought up numerous times, but nobody else cares to comment on. I can't push for that change alone, so since nobody else is willing to comment on it, it most likely will never be fixed.

 

Just consider it a negative perk of the Stalker. Highly unlikely it will ever be resolved.