Recently, I was doing the Spire of the Watcher solo because i wanted to challenge myself and to get "The Magnificent One" Triumph.
Midway trough, I had to eat but the game kicked me out of the game. "no problem i said, I'll just continue my checkpoint". So I'm at the end, kill Persys, get my loot. I get "One Class Town" & "Three Suns At Noon" Triump and i was telling myself where is the solo triumph. idk if its a bug or I'm stupid but i really don't want to do it again.
Edit: the triumph doesn't say anything without leaving or back to back. Plus i did made my fireteam go on closed, so no one joined.
Unfortunately, the triumph does want the run to be completed in full, without leaving, even if it may not directly mention it.
You'll have to run through the dungeon without leaving for the triumph to complete. I do agree the wording could be edited to mention it.