Bug with the attack speed of Earthquake

Im not sure if there is something else building into it, but I am a Titan Warrior dual wielding 2h maces and im using Earthquake for clear.

The speed of the initial attack is sometimes almost instant because of my attack speed but sometimes, without having any debuffs, it feels slower.
Like if the "normal" speed for my earthquake is 1 sec for the animation, it sometimes feel like the animation takes 1½ second instead. Like if im chilled or something without being affected by anything.

It happens even if im in hideout or not. Its like if I get chilled and it falls off, the slow effect for the animation of Earthquake is still in effect until a random time where it is super fast again.

Sorry for the bad explanation, not sure how to properly convey how it feels/looks.