Every now and then things get strange for no reason. Just happened.
FYI, I generated the source in Turbocad and exported the STL. That has been working fine on several dozen parts.
Now for strange. I just tried to repeat the process to get the images you asked for and got an absolutely normal looking support grid under that overhang. Whatever happened the first time won't repeat, no idea why.
Also FYI, I am actually using Repetier-Host at the top level. I selected the Cura engine within Repetier for the slicing since I was familiar with it from previously using Cura at top level. I assumed that slicing problems would be appropriate in this forum not withstanding not using the Cura front end.
So for now, the problem is gone by whatever means the computer gods saw fit to do to me.
Life goes on ...