Today, after a year of trying to get rid of thei problem, an Aperture "Craetive" at the Apple store found a way to correct it after contemplating it for about 15 seconds.
Here is the remedy:
To get rid of it, select image(s), go to Photo in the menu bar, hold down Option key, click on Generate Preview in the drop down menu. Wait for it to finish processing - a few seconds. Done.