Hi,
welcome @Anonymous.autodesk.com!
The file you have uploaded is different to that what you showed in the screenshot, in the screenshot the polyline is not closed:

And that can make the difference on the 4th vertex!
In case the polyline is closed a rectangle has 4 vertices and the closing segment/vertex would be drawn in the same way as the other 3 corners.
In case the polyline is not closed a rectangle has 5 vertices and so 2 vertices are at the same XY-position. That makes the difference for how the corner is represented.

- alfred -
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Alfred NESWADBA
ISH-Solutions GmbH / Ingenieur Studio HOLLAUS
www.ish-solutions.at ...
blog.ish-solutions.at ...
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CDay 2026------------------------------------------------------------------------------------
(not an Autodesk consultant)