It looks more like your drawing in Blender was already closed or cyclic and that your toggle was to open the drawing curve instead.
Adobe Illustrator is prone to creating multiple control points that will sometimes cause the curve to not know how to fill properly in 2d, and either moving the extra point a little will suddenly cause the fill to work or sometimes it is about using the Curve>Clean Up>Decimate Curve operator to eliminate extra control points not needed in the SVG.
That’s what the feature is meant to do. It either breaks a curve, or keeps it continuous. The same thing happens with curves created natively in Blender.