I'm able the create an etch in the sync mode but when trying in ordered I can't select the sketch elements on the plane of the tab.
Maybe the contour flange is the issue, I'm not sure. I went to your unbend and tried, no worky for me either.
You are very close to the solution. ;-)
You drew the sketch in the flat pattern. If you create the etch there it works. You only need to select "single" in staid of "chain":
After this you can select your sketch and the etch is made.
I don't upload the file because I work with ST8, so you can't open it.