When you do the Demonic Siege map, you'll often have an NPC helper with you (Linu, Bruenor, etc.). Especially if you have a habit of pulling multiple groups and fighting them all at once, I've noticed that Linu has a habit of wandering off, pulling a single enemy with her, and fighting a slow 1v1 dance. I've seen her pull an enemy half-way across the map this way. I had to track her down and finish the job myself, and then the final marker spawned unspawned and let me do the boss fight.
Perhaps something similar happened to you?
If you try re-entering the map does this issue persist?
Founding Member of "Wrong Side of the Stronghold" Ravenskya - TR / Krisha Chaos - OP / Waffles - GF / Dex Domitor - HR Becky the trendy GWF - GWF / Too Toasty - SW / Falcor - DC / Morrigan - CW / Sir Didymus - OP
Comments
Perhaps something similar happened to you?
If you try re-entering the map does this issue persist?
Ravenskya - TR / Krisha Chaos - OP / Waffles - GF / Dex Domitor - HR
Becky the trendy GWF - GWF / Too Toasty - SW / Falcor - DC / Morrigan - CW / Sir Didymus - OP