Hi Jean,

The line you mentioned in your initial post has lineweight assigned individually and its lineweight is 0.6 mm? plus it has color "by layer" and the Layer of the has "White" color or color #7.
But in CTB file you are using lineweight 0.25 mm assigned to the color #7, so the problem line is plotted with lineweight = 0.25 mm as assigned in CTB file.
If you will change color 7 lineweight in CTB file to "Use object lineweight", the line will be plotted with lineweight assigned to it "by layer" and will be 0.6 mm on paper.

Maxim