The latest version of Make It 2016 downloaded yesterday will not draw single lines. I am using latest El Capitan OSX on Mac and overtime I draw a line it is double. I try to delete on of the lines and they both disappear, If I persists I get a myriad of lines at various cut angles. I have deleted al library content and d reinstalled latest download to no avail. I can’t even easily revert to previous version now.
This sounds like a graphics card thing. Try this: Go to the SketchUp menu, left of File. Click Preferences>OpenGL and turn off Use Hardware Acceleration. Then close Preferences and try drawing some lines with the Line tool. Any change?