Group event near Crystalwept Groves in Iron Marches. Not possible to finish it and while it is running the karma merchant at the nearby heart is not offering his goods. Reminds you of the attacking army and tells you to stop it first.
Problem: According to the event description you need to kill his army first. Tried this and he had a few guys walking around him. Then the counter stopped at 7. Still 7 remaining to kill first. A lot of other branded enemies in the region but none seems to belong to the champion guy for the event and all the other walking with him are dead.
If you try to kill him now he always will regen health at empty health bar(1 hp). Not possible to kill him. Server Underworld. But could happen at other servers too since these kind of bugs tend to happen more than once and more often.