Can not download backups from freedombox

Running Freedombox 20.12.1 on a Raspberry Pi 3B+. I can make backups using the Backup feature. When I then try to download those backups, a new empty tab is opened in the browser but no file manager is started. The browser runs on my Linux box, running Ubuntu 18.04 LTS, from which I manage my Freedombox. Both Chrome and Brave give the same results. This used to work but has not since beginning of July.

In addition I tried downloading from a Windows machine, using Chrome and from my Android phone using both Chrome and Brave. Still no show, just an empty browser tab is shown.

Any ideas how to solve this?

(edit: This is a repost as the previous post was not in the right forum. I do not have the rights to delete the original post)