circular fillet and the others all work (see top 3 objects), just constant distance fails with the same objects at the bottom part of the screen dump. any idea why?

Maybe the sharp angles but wait Michael answer! :)

Hi Wim, currently constant distance on curves only works between line segments.

- Michael

I don't know why but get around is possible.
Just extrude it and then you can take edges which correspond what you need.

I know it's not very orthodox, but it's a trick.

Very cool trick! Bravo!

Thanks Michael!

Thanks Phiro, neat workaround indeed! that will solve the problem for now!