Kopano WebApp Files: Not showing files, but spinner "Loading files..."

This happend for all tested builds in the 8.3.0-master branch, sofar. The spinner never ends - no files shown.
Configuration GUI seems OK:

Tested with owncloud(nextcloud)-, smb- and ftp-accounts.
Account list shows green icons and reasonable version-information.

core-8.3.0~671_55.1-RHEL_6_PHP_56-x86_64
webapp-3.3.0.436_330-RHEL_6_PHP_56-noarch
files-0.5.0_30.1-RHEL_6_PHP_56-x86_64

python 2.6.6
fpm-fcgi 5.6.29
nginx/ 1.11.4

Best regards,
umgfoin.

OK figured that out:
Explicitly setting a cache-path in kopano-webapp/plugins/files/php/lib/phpfastcache/phpfastcache.php as described in KFP-102 will fix this issue.