Sebastian Schalipp

Thanks for your reply. It used to work fine until a week ago, using exactly the same plugins and theme, so a conflict is very unlikely.

It only stopped working after we have changed our WordPress root domain path from just domain to domain + subdirectory:

Before: https://www.wiras.de
Actual: https://www.wiras.de/verbundpartner

It seems that the script that generates the download files directory tree is now confused by the new subdirectory in the path. But where / how do we fix this?