I have had this problems since the alpha, and it has not gotten better. Approximately 60% of the time, my mouse clicks are not getting registered. Going to shoot: nothing, trying to aim down sights: nothing, trying to kick a door: nothing. This has nothing to do with ping/latency, as it happens even in the training/offline mode. All weapon types are affected as well as fire modes.
I was trying to get a friend to join me in the game and he was experiencing similar things. The only thing we have in common is we both have Corsair mice, different models but the same brand. This does not happen in any other game or in the original Insurgency, as I've checked to make sure its not my specific mouse.
I enjoy the game and still play it, but 80% of my deaths have been from my mouse clicks not registering and it's infuriating at this point.