If I'm the host in multiplayer they work fine. However, if I join someone elses game, they attack at normal speed (but make a sound as if they are attacking faster when I click faster). This has been tested with apothecary (increased weapon speed 1.5x) and Chaplain (increased weapon speed 1.5x) and even assault marine with perk (so 40% speed and 1.5x speed both) and none of htem attack faster when in someoen elses game.
I'll upload a video later/tomorrow if you're unable to replicate the bug.
EDIT: Friend on steam said he had same bug except he noted that the attack still registers, its just the animation that does not play. Can't confirm myself at the moment due to flying a spaceship in Elite Dangerous: Space Bus Simulator - lol