Still not consistently getting credit for the daily quest, even though I get an event chest. Last time it happened, I had just been bounced into the air, but this time I was on the floor DPSing away.
One additional thought, the Justicar spawned while I was doing the Bloodstone Champion event, which I completed. I arrived at the Justicar in time to finish the 50% event (kill the vengeful spirits) and then complete the last 50% of the boss. IIRC, the last time it bugged I finished the Bloodstone Champion event immediately before Justicar as well.