Killed several rares in the Everfrost dungeons and no credit received even after relogging on toons. This is occurring on Rizlona.
Following this for later, I have 1 left in Arena of Chance to be done with that expansion and I don't plan on wasting another day trying to get an instance with it to pop only to not get credit.
LDoN is notorious for mobs killing themselves on non-damage sources, which won't credit you, because all our buffs are so much damage now. You have to do at least 1 damage to get credit/exp/loot off a mob. Take off all DS sources, if you have a pet turn on /pet spellhold. Make sure you are doing at least 1 damage to the mob first.
It is working fine for me on Rizlona. Are you doing hard difficulty dungeons at level 65? That's the only way you get the hunter achievements.