This is the result of issues with the adapted control scheme of the ported game. The PC version of Dark Souls II is known to have issues when it comes performing jumping attacks and guard breaks.
Guard breaking when unarmed or using a fist weapon is significantly faster than guard breaking with any other weapon, and can be accomplished with nearly all weapons. If the target's shield is up, their guard is broken: they are stunned for a longer period of time, during which the player can perform a Frontal Riposte on them. After a short windup, the player delivers a backhand attack, stunning their target.
The Guard Break move replaces the kick from Dark Souls. 2.3 Making Guard Break and Jump Attack work on PC with gamepad using Joy2Key.
