Can not download backups

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.

Any ideas how to solve this?