Sometimes I swing my sword and the robot just goes right through it with no damage. Also sometimes when I jump and do a vertical swing it just had no effect on them.
Human! You are about to become a sword robot! · By
I've filed a bug for the power attack hit detection. As far as not doing damage with other attacks, try following through with the mouse when you use a horizontal attack. Strafe attacks are some of the most likely to connect, and strafing in general keeps the archers guessing.
Hope that helps a little.
-Cheers