Hey
In my experience in the expedition playlist, the ruffians spawn at the end of a treasure step and despawn when the last treasure engram is collected.
So most of the times they despawn before the heads-up telling you they have spawned.
So my suggestion is to make the ruffian stay after the treasure step or spawn earlier so the team have time to react and not accidently clear the step.
Also with the amount of treasure engrams ruffians are really useless.
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I didn't know these were even a thing until I saw one this morning, and that's after a ton of Expeditions the past week. Bungie probably should have made killing them necessary to proceed or something.