I have completed 9/10 triumphs, and the only one left is to win a gambit match with all gambit weapons.
I have used Breakneck/Malfeasance, Hush, and 21% Delirium. I also used full sentry armor, and the triumph did not complete.
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Breakneck, Hush and 21% Delirium do not count. Use weapons that appear on the Gambit collection badge. I used Parcel of Stardust, Trust and Bad Omens. If you don't have Parcel, Malfeasance will work in that slot.