I've been reading pages of "Expand Stroke does not work" and in hope that someone had a decent solution. My journey started because I can't get even reasonable results for an export to svg, so I thought I'd 'simply outline the stroke' and then export. Boy was I wrong.
The sharp lines (a curve) is the original and the rounded one an arbitrary 'guess' from the Expand Stroke "command". Some things should be noted, the points are not straight nor equal.
I should say to accomplish my task (export to SVG) I exported to JPG (which worked great!), used an online tool, and within 25sec I had completed that tasking downloaded an identical svg file - sadly not within Designer. I know there are a lot of things in software that can (and will) go wrong, but maybe we done need 'personas' but properly functioning commands?
Just for giggles I did upload an afdesign file. Let's just hope it was user error (me) and I don't know how to use Designer.
project_Line_test.afdesign