I've played the new Arms Dealer (Heroic) Nightfall four times over the last two days. The first session, during the very first ball running phase, my game hard crashed to desktop. When I logged back in I rejoined the session and finished it out. My next two NFs, I had no bugs. Then my fourth, during the very first ball running phase again, my game hard crashed to desktop. This time when I logged back in, I wasn't able to re-join and I lost vanguard rank progress. This is the only hard-crash I've had in Destiny (that I can remember) in months, definitely since Lightfall launched. The fact that it's in the exact same phase of the Nightfall has me wondering if there's something bugged.