The problem still exists. I have Seblod version 3.20.1. The update site is: https://update.seblod.com/pkg_cck.xml. Joomla does not offer me Seblod update 3.20.2. I can download the update package, but I don't understand why Joomla does not offer me the Seblod update.
If the software cannot be updated, it is a very worrying sign for everyone (me including) who believed in the product so much that they based their business on it. :(
The XML was not up-to-date indeed, but it doesn't mean that you can't update your app/site. You can download manually from the home page, and upload to update.
Now the XML has been updated, you should see it from the auto-update.