I reported it awhile back, and it’s been a bug for months. Nerub-ar Palace Raid - A Queens Fall.
The boss called" The Silken Court" bugs and you can’t go to the next boss because one of the bosses disappears. So than it counts as a kill with no loot and doesn’t trigger the great vault. This has to be something to fix this, or a work around. Either way its annoying, and disappointing to get screwed out of loot, and great vault each week because of this bug that should have been fixed months ago. It also keeps you in battle so you can’t teleport out and if you leave the group before others, you catch the coward debuff. Come on now!