We got him to under 20% only for him to just reset. It was our first attempt at trying to kill him. Our dps was not great , so I am wondering if there is some kind of timer / death count on the fight that may have caused this ?
It's not bugged, you most likely had an add go under the world and run off some crazy way and reset the encounter. It can happen on many encounters with adds but it is rare. If you keep having it happen, it could be because either the tank spot or the raid is positioned somewhere strange.
He and his adds have a leash range, and I think there is a penalty if you pull him too far from his spawn location. I remember the first time we pulled him we tried positioning to the absolute maximum distance from the assassin spawn, and there was a penalty related to the assassin not able to find us in an expected amount of time. Other than that, I know our guild has killed it several times this week, so don't think its bugged.
That is exactly what it is. The Assassin can cause this if it goes under the world. Also if you have someone too far away, there will be a red message about the assassin teleporting to someone and that causes all kinds of issues.
