EDIT:
PROBLEM SOLVED!
I replaced the core folder with a new one and deleted my browser cache. Now it works again.
It seems that my Web-Interface is broken. It looks like no CSS / JS is loaded and just Text is displayed.
I cannot click anything or use it somehow but the desktop client syncs without problems and I can access all files via the mobile app.
Does anyone know how i can fix the webinterface?
Nextcloud version: 10.0.0.29
Operating system and version: Rasbian Jessie Lite 4.9
Apache or nginx version: 2.4.10
PHP version: 5.6.3
Is this the first time you’ve seen this error?: Yes
config.php:
<?php $CONFIG = array ( 'instanceid' => 'xxxxxx', 'passwordsalt' => 'xxxxxx', 'secret' => 'xxxxxx', 'trusted_domains' => array ( 0 => 'xxxxxx', ), 'datadirectory' => '/var/www/nextcloud/data', 'overwrite.cli.url' => 'xxxxxx', 'dbtype' => 'mysql', 'version' => '12.0.0.29', 'dbname' => 'xxxxxx', 'dbhost' => 'localhost', 'dbport' => '', 'dbtableprefix' => 'oc_', 'dbuser' => 'xxxxxx', 'dbpassword' => 'xxxxxx', 'installed' => true, 'memcache.local' => '\\OC\\Memcache\\APCu', 'maintenance' => false, );