Took me a little while to figure out but now I know: You have added radial transparency to all the lines.There have been changes made to how transparencies work between X6 and 2020, which may explain why you don't get the result you expect.May be a bug, I don't know, but this is most likely the reason.
what type of bug in 2020 or x6. how to solve it.
I didn't say it was a bug in either of them, they just work differently and some unwanted effects may occur.In 2020 you can make transparencies elliptical and rectangular for example, not only circular and square.How to solve it?One way to correct it seems to be to enable Free Scale and Skew (Property Bar when Transparency tool is active.Not 100% sure what effect you're trying to achieve but adding a circular transparency to 84 outlines sounds like a pretty bad idea to me.I would start by grouping or combining the lines first of all, then I would use linear transparency instead of circular.Linear is easier to render apparently and the appearance will be the same in this case.