Bug quest dungeon for 5th ark had to be done twice

It was around a week or two ago, my bad that I didn’t do this at that moment. Once I cleaned the dungeon for the 5th ark in the mirror dungeon I think, where there are ice golems, once I killed the demon commander and took the ark and got out of the dungeon with the music, I saw that the mission notification was still on the dungeon and had to clean the dungeon the exact same way a second time. Don’t know what triggered it, I don’t think I did anything special. I was told to report the bug here.