As said in the title, sometimes the 2nd heavy attack of the chain axe is longer than intended, mostly happen if you do heavy attacks in succession: the animation, instead of just lifting the axe, will be like this: the axe will be lifter a bit, dropped, and the animation will beging again from scratch; this make the 2nd heavy attack a good half a second longer when it happens.
I will try to make a video of the issue