SharePoint Hub Site Association not working for Sub Site anymore

Earlier we were able to use the PowerShell commands and associate Sub Sites from another Site Collection successfully to our Hub Site. This has worked up until very recently (last month), but now nothing happens when we run the exact same commands. No error shows, but there is no effect either. What has happened and why is it not working anymore?

In the modern SharePoint Admin center we see that the Site Collection main site is associated to the Hub, but apparently the effect is not trickled down to Sub Sites. Again, earlier we were able to do this by running the PowerShell commands for the specific Sub Site to get the association created.