I just bought a Leica M6 a week ago, and developed the first and second roll I took. The photos in the first roll showed no problem, but the in the second roll, the first, second, and third photo is showing the vertical light leak. Later photos of third photos are totally fine. I cannot guess what's the problem.... Do somebody know what is the cause of this issue? p.s. this roll is tri-x400
The light leak only appears on one of two rolls of film: This suggests the problem is not the camera.
The light leak only appears on the first three images: This would suggest to me either a film handling issue, or a minor issue with the film cartridge.
I would try another couple of rolls of film to see if the problem re-occurs, if it does not than the leak was something specific to that roll of film.