During an intermission in the Halls of the Damned (NMD 47), when I moved to the outer edges of the room, the entire event despawned and reset.
The intermission was the “click the two switches” variation, and the enemies were skeletons. The room itself was unusually large with two extended sections on the left and right sides; if I moved into either of these extensions, all the skeletons and the switches/spikes disappeared. As soon as I moved back toward the center of the room, the event reappeared as new.
I was able to repeat this basically endlessly, though I didn’t check to see if the mobs were awarding any experience (currently, intermission mobs are often bugged and don’t reward experience when killed). Once I finished the intermission by clicking both switches, the phenomenon ceased to occur.