Looks like I was able to resolve the issue. I had to change the setting, Files >> download remote images to local. This is now enabled. I tested by disabling creating a topic. Reenable, create a duplicate topic. Next I checked the thumbnail image in both topics. One is referencing the local image store. The other is referencing the remote image from the link.
Next I sharing each topic to a social network, linked-in cause the preview works. In the case with the local image store. The LinkedIn preview picks-up the local image from my community. The other gives serves the opengraph_image from settings and not the thumbnail image from the link site.
So, it appears I need to have the setting, Files >> download remote images to local, enabled to show the preview image from onebox propagated to the social network when sharing links.