Multiple Filedownload, 403 Forbidden

Hi there.

I wasnt able to find a related post so here is a new one.

After setting up a new instance of Nextcloud and some post-deployment configurations like SSL I tested the new Cloud. File upload wasnt a problem but when im trying to download multiple Files (2+) appears a message 403 Forbidden:

2017-08-29 13_04_05-403 Forbidden

I tried the same procedure on other browser (chrome, FF) but with the same result. single-file Download is no problem, even the multiple Download of example images of Nextcloud works fine, but not for uploaded files.

I have absoluteley no idea where the fault is. I checked every config-file i could find.

The permissions are set to the www-data user:

chown -R www-data:www-data /var/www/Nextcloud/
chown -R www-data:www-data /path-to-Nextcloud-data-store/
Read and write permission are also set for both Directories and Subdirectories.

To the Setup:

Hyper-V Host with Windows Server 2012r2

Ubuntu Server 16.04 LTS

Apache 2.4.18
MariaDB 10.0.31
PHP 7.0.22-2

The Nextcloudserver is located behind a Sophos SG Firewall. The Firewallprofile for this Nextcloud is set β€œAny” in both directions to make sure theres no problem.

Any help would be highly appreciated!!