Filebrowser thumbnails "can not create img for private://" I am using Drupal 8.7.5 and PHP 7.3.7 running on Apache 2.4.6. 

UPDATE: I'm trying to make available a library of images to the public. I chose the content type of 'Directory listing' to do this. In the Directory listing I have configured a private file path (i.e. located outside of Web root) to hold the images. Apparently I have done something right as it is working except for the thumbnails. I get constant 404 errors in my apache logs and the other errors through the web interface seen in the images below.

What have I missed in terms of getting the thumbnails working? Am I missing an binary or library to render the thumbnails? Did I not create or configure a path for the thumbnails?

Below are some of the steps I have done to configure the Directory listing.

UPDATE On the server I have installed Druapl 8 using composer and drush to $APACHE_CONTENT/drupal. The drush site-install then goes to $APACHE_CONTENT/drupal/web (drupal app_root) and have added a 'private' path as $APACHE_CONTENT/resources. This puts the 'private' path outside of the drupal site's DocumentRoot. The permissions and ownership for the 'private' path are 775 and apache.apache. Also, a .htaccess file was auto generated for the 'private' path. It contains the following:

# cat .htaccess
# Deny all requests from Apache 2.4+.
&lt;IfModule mod_authz_core.c&gt;
  Require all denied
&lt;/IfModule&gt;

# Deny all requests from Apache 2.0-2.2.
&lt;IfModule !mod_authz_core.c&gt;
  Deny from all
&lt;/IfModule&gt;

# Turn off all options we don't need.
Options -Indexes -ExecCGI -Includes -MultiViews

# Set the catch-all handler to prevent scripts from being executed.
SetHandler Drupal_Security_Do_Not_Remove_See_SA_2006_006
&lt;Files *&gt;
  # Override the handler again if we're run later in the evaluation list.
  SetHandler Drupal_Security_Do_Not_Remove_See_SA_2013_003
&lt;/Files&gt;

# If we know how to do it safely, disable the PHP engine entirely.
&lt;IfModule mod_php5.c&gt;
  php_flag engine off
&lt;/IfModule&gt;


In drupal/sites/default/settings.php I have:

$settings['file_private_path'] = $app_root . '/../../resources';


Viewing the Configuration->Media->File system is see:



I've configured a private file path to use with content created via 
Content->Add Content->Directory listing. 



I have then used scp to copy files into the private path.

Through the web interface, I can browse through the content but I never see the thumbnails. I get errors above my content. 



In the apache logs I see 404s for the thumbnails:

GET /system/files/styles/thumbnail/private/Images/JPG/Marshal_Hub.jpg?itok=QwQds55m HTTP/1.1" 404 11730


I have GD installed. 



While I can browse all of the content in the 'private' paths, none of the thumbnails get generated.

What do I need to do to get the thumbnails working?
This is a workaround I used to solve the issue:

[https://www.drupal.org/project/private_files_download_permission]

I don't consider this 'magic' to be a fix. There is a lack of documentation and/or a bug in the filebrowser module.

How can one raise an issue with the developers?

PS: Also, now have another issue with the filebrowser module: sort order is not being honoured in Grid view!