Page margin: spurious line running from top right-hand edge to the page border
OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 188.8.131.5292, revision: c2bfca4
Open any score. Select the view menu and tick "Show page margins." Depending on the "First page number" (Format > Page Settings), on either the even or odd pages you will see a spurious line running from the top right-hand edge of the page margin to the page edge.