Good day, I don't know how to ask Google about it so I'm seeking for help here.

I made wall decor for The Sims 4 - a painting to be more precise. It's the second time I try to make painting and I get the same problem in other variation. The objects itself looks good in both - Blender and S4S. In game there appear glossy lines on the top and in the middle of what supposed to be canvas. Some time ago I made recolors of ingame paintings and I didn't have this kind of problem. So I can't understand where I made mistake: in my mesh, in texture I used or in the way I replaced the object in the game with my mesh. I saw this kind of problem on someone's else work as well, but I can't ask them what may cause it because they didn't fix their piece of CC and seems inactive for now.

Hello, chances are I think it has to do either with the normal map or specular map files located in the warehouse section labeled as dst
Just overwrite the files with a solid neutral grey image as a .png ( but not the file that shows your texture image- usually the first DST on the list)
And see if that changes anything maybe?

Thank you for respond (:
So, I changed first DST file as you said and it gave me nothing. Then I replaced second DST file and these lines really disappeared. But it gave other effect: now paintings look like canvas behind the glass and frame itself is covered with varnish. This is clearly visible in comparison with the picture on the left by another author:



And it's the exact same thing which I have on my other custom painting - it hasn't any marks, but it also looks glass/metallic. It doesn't bother me a lot, but under certain angles you can't see the canvas and what depicted on it. Below I attach a couple of screenshots: on the first are the files that were before replacement, on the second are the replaced files.