I’ve just tried configuring the theme component with exactly the same settings are were posted above. It is working for me, so I don’t think there is a bug in the theme component.
If you are able to open your browser’s web inspector to its console tab, do you see any errors appear in the console after you click the “share” button?
Can you try opening your site in safe-mode to see if the missing icons are a result of a site customization?