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 noticed this too. Its even worse if you have someone doing the throw exploit to constantly throw the same treasure and each one count, making the progress go up faster.