[SOLVED] User can login via web interface, but not via WebDAV / WebDAV very slow, how to debug?

Nextcloud version: 11.0.2 (stable)
Operating system and version: Docker on Arch Linux
Nextcloud: Docker nextcloud:11-fpm
Apache or nginx version: Docker nginx:1.11.10
DB: Docker mariadb:10.1.22

When trying to sync a with DavDroid on a Smartphone connected to WLAN, I get this in the error log:

Debug	webdav	Sabre\DAV\Exception\NotAuthenticated: HTTP/1.1 401 Username or password was incorrect	2017-04-02T13:34:50+0200
Info	core	Bruteforce attempt from "" detected for action "login".	2017-04-02T13:34:50+0200
Warning	core	Login failed: 'ping' (Remote IP: '')

ping is the username, and I am able to log in with this user and password just fine.
When I try to connect using this user in the Nextcloud app, it won’t work as well, saying “Server is taking to long to respond”, but I get the message “User or password invalid” in the error log.

Another user I have is able to sync fine via DavDroid, BUT it is dog slow. It needs over 2 minutes to sync contacts and five calendars over WLAN, with the CPU sitting at 5% all the time.

Any pointer on how to debug this?

The NGINX config I use is this: https://github.com/nextcloud/docker/blob/master/.examples/nginx.conf

config.php goes like this:

$CONFIG = array (
  'instanceid' => 'xxx',
  'passwordsalt' => 'xxx',
  'secret' => 'xxx',
  'trusted_domains' => 
  array (
    0 => 'mydomain',
  'datadirectory' => '/var/www/html/data',
  'overwrite.cli.url' => 'https://mydomain',
  'dbtype' => 'mysql',
  'version' => '',
  'dbname' => 'nextcloud',
  'dbhost' => 'db',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'oc_spheenik',
  'dbpassword' => 'xxx',
  'logtimezone' => 'UTC',
  'installed' => true,
  'mail_smtpmode' => 'php',
  'loglevel' => 0,
  'memcache.local' => '\OC\Memcache\APCu',

For bruteforce detection:

If you have two-factor authentication active, make sure that you create app-password (on personal page) for each directly connected webdav device (calDAV, webDAV, or any of the desktop or mobile clients).

Thanks a lot!
I deleted the entries in that throttling table, and disabled the feature, since my installation is behind a proxy and does always detect the same IP (the one from the proxy, maybe one can change that somehow).

Oh and I found the problem with not being able to login. It’s embarrassing, but there was a “l” instead of an “I” in the password.