We have made some changes to Line Styles in 11.0 This affects how they look in:
Both line thickness and the look of stippled lines (dot, dash, dash-dot etc) are affected. The default thickness of solid lines should look the same as before.
Note that this will affect any PDF DIFF Tests with references made before 11.0. If you have any references with lines for PDF Diff Tests made before 11.0, the different line styles will cause the diff test to fail if run in 11.0. You will need to make new references in 11.0 for those tests.
You may find more information and some comparison images on this page.