Sword Wave Buggy?
This come from the problem they have with projectiles. Sadly 3rd AA of sword is a triple projectile attack, which make it buggy against almost every structure, sometime it will go off 3 time in a row without hitting anything.
For any boss with reflect and structure stick to Greatsword for now.
It’s because the attack uses (short range) projectiles, they don’t deal with z-axis very well and inanimate objects also have a tendency to be placed slightly underground or at least at a different height to the spot your character aims at.
There isn’t really anything you can do about it except use another weapon; same goes for the rare fights where enemies reflect projectiles.