About the above event, taking place in the fields of ruin and according to the wiki, that particular area is called Warrior’s Crown.
The event consists of killing 6 ‘assassins’ (strong separatist mobs) and their leader.
As support, 6 NPC’s will be there to fight them.
The bug is that none of the NPCs take damage. They stay at full health when hit by the mobs, even when they are knocked back etc. (Local does are often pulled into the fight, and those don’t damage them either).
I have been there twice now and it is the same every time. The commander of the little NPC squad did die normally the first time, but was invincible the second time.