I only had it happen once, after the April Update. I took a Smite of Merain w/ Firefly into the Malok Strike. I crashed MULTIPLE PLAYERS' Destiny clients when I Firefly'd a Taken Phalanx in the room just before the Shrine of Oryx Boss Arena. It was me and the Fireteam Leader, I think one guy was lucky enough to be a zone away. So yes, it can happen as recent as the April Update, with no noticeable fix in sight. Hopefully they can come up with something better than Firefly for the Rise of Iron Raid. Otherwise people are going to be pissed if they crash their client Mid-Boss just because it wasn't fixed. I'm surprised this doesn't happen in PvP though.

I've been told that it happens when Firefly is working in conjunction with another damage modifier perk. Back when The Taken King first came out, I bought The Vanity from FWC which had Luck in the Chamber and Firefly on it. I specifically bought it for the Firefly perk so I obviously activated that node, it was impossible to bypass the Luck in the Camber node ( it had to be activated in order to continue upgrading the weapon so I had to have LitC on. Those 2 perks together would crash the game every dozen or so critical kills.

That explains why I crashed during a Nightfall then. Smite of Merain + Small Arms* = Boom-Crash. So it's ALL damage modifiers, not just perk-based but also playlist- based. Interesting.