My fireteam did a Garden of Salvation flawless today but none of us got the triumph for it. We didn't utilize any cheese, everything was done legit. The only thing maybe, is that we had two people pull for 2nd and boss encounter to skip jumping puzzles (I've heard somewhere that this can affect it, but not sure). But no joining allies, no one left and rejoined and no one disconnected. I attached a URL of my raid report of the flawless run.