Date & Time: June 25, 2022. 1:48 PM BRT
Frequency: Only once
World name: Lamia
Character name: Peter Panic
Class/Level: Dancer 77
Party or solo: Party, 4 people
In-game time: 1:17 PM
Area and coordinates: Main Scenario Duty The Porta Decumana
Steps:

1. Joined the ongoing duty after someone left the party.
2. A cutscene had already begun when I entered the duty, which caused me to miss it and let me free to roam the area while everyone else watched it.
3. When the cutscene ended the other members were teleported to another place, to fight the boss, and I was left behind in the first area.
4. I wasn't teleported to the fight after it began, since it didn't trigger the usual 15 seconds countdown to lock the instance. I also couldn't use Return.
5. After the other members died the fight wouldn't reset. Since I was alive in another place and the boss couldn't kill me, it wasn't a wipe.
6. By the end I thought that by leaving they would be able to continue, but they chose to disband.

Couple of screenshots of me, alone, while the rest went to fight the boss:

https://i.imgur.com/SXrqz1O.png
https://i.imgur.com/bARoDI6.png