I went through the dungeon alone and waited for the mission completion timer. Triumph for solo wasn't given. Why? See my Titan.
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Greetings! Your solo run is registered as completed from a checkpoint. The triumph wants the run to be completed from start to finish, without leaving the instance. Unfortunately, you'll have to run through the dungeon again from the beginning, without leaving. https://dungeon.report/pgcr/12391785847