When attempting to investigate the disappearing buskers, the notable items appear to be wine, bloodstain, broken instrument, then a note read near the instrument. Online walkthroughs bear this out.
My attempts to advance the quest by reading the note do not work. After reading the note, no voice lines are triggered, and the quest does not advance further.
This bug recreates repeatedly, even after reloading a save and restarting the quest. In case it matters, my current companions are Neve and Harding.
I have this problem too. Think I had neve and lucanis. I've come back to it after other quests and closing down the game, this time with neve and bellara and still can't progress.
Retried it today, and a fourth interactive was added to the three already outside, more bottles. Interacting with them allowed the quest to advance. I'm not sure if they fixed something, or going with different companions / after a game restart / after a map reload fixed it.
Came back to say the same haha, an extra investigation spot came up on the level just outside the bar although the search radius was still showing as by the dock, and I was finally able to progress
