I have created a footprint in which the rounded ends of the left and right hand top layer pads are to be squared off by removing them using a pair of top layer Solid Region set to No Solid. I the screenshot below, the upper No Solid region is highlighted. The lower region can be seen as a thin red line.  The problem is that the gerber files show that the No Solid regions are having no effect:  The image above is from gerbv. The JLCPCB viewer shows the same: the rounded ends are not cut off by the No Solid region.