Can not add new users

Hello my nextcloud is running fine (latest stable)

Nextcloud version 12.0.3
Operating system and versionUbuntu 16.04
caddy
PHP 7.1.9
Is this the first time you’ve seen this error?: yes

Can you reliably replicate it? yes
If I am trying to add a new user (independent if a group is added or not) nothing happens if Iam pressing add button.
no entries in log to find?

docker nginx log
2017/11/29 18:57:35 [error] 305#305: *12404 directory index of “/config/www/nextcloud/core/doc/user/_static/” is forbidden, client: 172.17.0.1, server: _, request: “GET /core/doc/user/_static/ HTTP/1.1”, host: “nextcloud.dddd.de”, referrer: “https://nextcloud.dddd.de/core/doc/user/index.html

docker php log:
empty

The output of your config.php

<?php $CONFIG = array ( 'memcache.local' => '\\OC\\Memcache\\APCu', 'datadirectory' => '/data', 'instanceid' => 'oc7vlpufun4k', 'passwordsalt' => '', 'secret' => '', 'trusted_domains' => array ( 0 => '192.168.100.10:82', 1 => 'nextcloud.dddd.de', 2 => '192.168.100.10:4432', ), 'overwrite.cli.url' => 'https://nextcloud.dddd.de', 'overwritehost' => 'nextcloud.dddd.de', 'overwriteprotocol' => 'https', 'dbtype' => 'mysql', 'version' => '12.0.3.3', 'dbname' => 'nextcloud', 'dbname' => 'nextcloud', 'dbhost' => '192.168.100.10', 'dbport' => '', 'dbtableprefix' => 'oc_', 'dbuser' => 'nextcloud', 'dbpassword' => '', 'logtimezone' => 'UTC', 'installed' => true, 'mail_smtpmode' => 'smtp', 'mail_smtpauth' => 1, 'mail_smtpauthtype' => 'LOGIN', 'mail_smtphost' => 'ASD', 'mail_smtpport' => '465', 'mail_smtpsecure' => 'ssl', 'mail_smtpname' => 'AsdASD', 'mail_smtppassword' => 'asdasd', 'mail_from_address' => 'cloud', 'mail_domain' => 'ASDAsd', 'updater.release.channel' => 'stable', 'maintenance' => false, 'theme' => '', 'loglevel' => 2, );

You can enable the debug mode for more information:
https://docs.nextcloud.com/server/12/developer_manual/general/debugging.html