The last step of that mission has me fight me way down towards Lancelot and Nimue.

The goal is to kill Lancelot. 

When i approach Lancelot Nimue says a few lines and then Lancelot does. Unfortunateley Nimue decides to teleport out of the encounter area and stands about 2 steps away from the barrier. This would not be a problem if the encounter ended with Lancelots death, but it does not. 

The game expects Nimue to die, but she stands outside the designated area for the encounter and i could only finish the encounter and the mission because my thunderstorm's area was large enough to hit and eventually kill Nimue.