Cannot update to 18.48

I have a virtualmin server that I recently updated from authentic 18.40 to 18.47. Now the system information panel reports that 18.48 is available. If i click the update button the panel goes blank and a red progress bar moves across the top, but in the end it still reports I am on 18.47 and 18.48 is available. I tried downloading the theme and then updating at Webmin Themes | Install theme. When I select "From uploaded file" and enter the file in the box beside it, clicking the Install Theme button does nothing. When I select "From ftp or http URL" and enter https://github.com/qooob/authentic-theme/releases/download/18.48/authent... in the box beside it, clicking the Install Theme button does nothing.

How can I update to 18.48?