It seems that easy themes has influence on downloads in unpublished folders.
They do not work properly when easy themes is installed.
I have experienced these problems in multiple installations now and as soon as et is deinstalled the download works.
Environment:
php 7.4
Contao Version > 4.4.28 and 4.9 all Versions.
Perhaps it is worth checking as I have detected no other correlations as a cause.
Just a message "failed to download" in the browser.
I have just updated easy-themes from 2.2.8 to 2.2.11.
That solved the problem in on installation now.
It seems that easy themes has influence on downloads in unpublished folders.
They do not work properly when easy themes is installed. I have experienced these problems in multiple installations now and as soon as et is deinstalled the download works.
Environment: php 7.4 Contao Version > 4.4.28 and 4.9 all Versions.
Perhaps it is worth checking as I have detected no other correlations as a cause.