The Background add to Hub Site is not Displaying on Associated Sites

I had a communication site converted to a hub site and added a background image to it. This background image is not displaying on the sites that I've associated to the hub site. I've 

• Removed associated sites, added background, re-associated sites
  • Even waited 24 hours to see if there is a change
• Added the same background to the associated sites
  • This doesn't stick of course since it's supposed to adopt the hub site format
• Tried different backgrounds and formats with the same result

The background was not on the site when it was converted, the conversion was by PowerShell and the background was added using the SharePoint UI.

What gives?!