This bug has been around since the changes which gave kill credits to healers/tankers. As I do not play normal shards, I cannot confirm that it exists outside of Siege Perilous. When fighting monsters such as Corgul or Scalis, upon the creature's death it will frequently be the case that only one person gets looting rights even though others present have done plenty of damage themselves. This appears to happen whether the participants are partied or not. The person who gets sole rights seems fairly random (not necessarily the top attacker or a particular type of character). Such a bug means that only one person receives an artifact drop, or chance thereof, and makes doing these sorts of monsters fairly pointless. My group of nine tested this again today with Corgul. In the first attempt, run in a party, only one member obtained looting rights. In the second, done without party, all members obtained rights. In a similar manner, it is also now not unusual to see one person obtain all six power scrolls at a champion spawn.