Photos would help.

Have exactly the same problem. I am baffled as I have never seen this dark strip down seams ever before. Has amyone any idea what causes this. It is a champagne colour vinyl yet the seams are much darker. I was told they hadn't dried but that was a week ago and they are still the same?

ylesyoung - I was told that as well! I tried washing the seams, going up and down with a sponge and soapy water to remove any residue that could be producing the discolouration, and it may have helped slightly but the problem still persists several months later. There are two seams that are perfect so I suspect that too much paste was used for the others and it penetrated the paper, though mine is a heavy duty, scrubbable vinyl. I didn't post photos as it is subtle and doesn't really show the problem, but it is noticeable in person and still bothers me!

My problem is identical to yours. I had to put a lot of paste onto the seams as they were curling up. I have wall papered for many years and never came across the likes of this. My paper is a heavy duty vinyl so it looks like there is no cure. I suspected it may have been excess paste.

Holy smokes. This is the EXACT same paper [has to be the same manufacturer] I am having this problem with. I have done a lot of wallpapering and have never seen this. My quality control while installing could not have been tighter. I did notice the glue was ornery but my application process was consistent. Most seams show. Some not at all. It's in a basement.

Q: is this still a problem after 3 months? The only explanation is moisture wicked in the edge between layers.

Note. The picture is a week old. Seams have gotten better but are not invisible yet

Just windering if the lines ever went away or if you found any solution that might have helped Thanks!