If I attack someone, it won't do fast attacks most of the time. I don't know what triggers it, but it seemingly at random changes between clicks fast attacks and holding the mouse being a defensive stance, and clicks being slower attacks that aren't useful. When the clicks do that, holding the mouse results in a flourishing swing that does absolutely nothing.
What causes the switch between these two modes? I'm still moving as if I'm locked on, and when I'm not locked on I attack and move in a different way.
This is on PC, if you didn't figure that out from the "holding the mouse" thing.