There has always been problems with mobs turning invuln when they shouldn’t but it wasn’t in a critically important way.
But the harpies in FotM are doing it regularly now. I have attacked them from around 500 ft and also right next to them and it said invulnerable. At one point, our entire party, including melees could do no damage to one. It happens to vampire bats sometimes in the grawl fractal.
We tried different things trying to avoid it happening but it kept happening.
A mechanic to prevent cheesing a fractal should never block progress of legit players.
By the way, if they are invuln and blocked from combat from me, why the kitten are they still able to attack me??
This is one of those long-overdue needed fixes.