Flurry is only supposed to go on cooldown if any of the 3 strikes miss or deal no damage, but if electroshock module damage (or most likely energy edge damage, too) happens to kill the enemy before the last hit, flurry will go on cooldown and cost reduction stacks will be removed. This is accompanied by the "ding" sound effect that normally happens when all damage is resisted, even though it's not, the target is simply dead and there's nothing to hit anymore, which would normally result in no cooldown/stacks removal.
I suspect the game thinks that, since the mechanical damage of the hit didn't kill the target, flurry isn't over yet, but the target is dead and there can be no next hit, so it interprets it as a hit with no damage, that's why the "ding" sound plays.
Supposedly, someone told me this is also the case with spikes on armor, though I didn't test that myself.
I attached a short webm.
