Vanishing mob bug?

ProfessorKittyhawk

Today is the first day I've resumed playing on an alt (or playing in general) since the IC update. But something I've noticed is some mobs seemingly vanishing in mid-fight, but their health bars remain and they can continue attacking. I, however, cannot attack them. They seem to fade in and out, like they're going between instances or something. I've never seen a bug lIke this before. I filed a report in game and a friend told me she'd seen something like that since the update as well. Just wondering how widespread it is and what the problem might be. I disabled what few add-ons I use off, but nothing changed. The quest I was doing when I first encountered this issue was Merriment and Mystery in Eastmarch, where you fight the goblins. Happens to regular mobs and the boss even, to the point I can't seem to kill the boss. It's quite frustrating.

Also, sorry if there's a topic about this already. Tried searching but found nothing pertaining to this. <_<