Safari top sites thumbnails not updating

Good Day:

I've been having an issue for a while with the Safari top sites feature. Some of the website thumbnails on the top sites page do not update. This doesn't seem to be a problem with the individual sites since, on another Mac running the same OS and Safari, the sites DO update.

I've searched and found several old posts regarding this issue recommending refreshing the sites. This does not seem to work for me. I have refreshed multiple problem sites both by hitting the refresh icon in the address bar and by using the shortcut key combination of Command+R. While the site refreshes in the browser, the thumbnail does not. Some answers seem to indicate refreshing while on the top sites page. I have not been able to do this since, when on the top sites page, there is no refresh icon in the address bar and, alternatively, when hitting Command+R there appears to be no action.

I've also tried deleting one of the 'problem' sites from the top sites list and then re-adding with the result being that the new thumbnail for that site is now only white space.

Any suggestions would be appreciated. Thanks.

-Ed