When I try to create a user in WordPress, the download of the file "user-new.php" starts. But no user is created. The same problem if I want to change the settings. Then the download of "options.php" starts
This is the content of downloaded options.php:
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>503 Service Unavailable</title>
</head><body>
<h1>Service Unavailable</h1>
<p>The server is temporarily unable to service your
request due to maintenance downtime or capacity
problems. Please try again later.</p>
</body></html>
Error log from the provider:
30.10.2018 16:45:01 example.org [client 2a01:c23:9000::] rdbm_handle_postscan_block: hostname=example.org, client_ip='2a01:c23:9027:b800:34b5:9469:33f9:1ef4', would captcha uri: '/wp-admin/options.php'
30.10.2018 16:53:58 example.org [client 2a01:c23:9000::] rdbm_handle_postscan_block: hostname=example.org, client_ip='2a01:c23:9027:b800:34b5:9469:33f9:1ef4', would captcha uri: '/wp-admin/options.php'
30.10.2018 17:01:23 example.org [client 2a01:c23:9000::] rdbm_handle_postscan_block: hostname=example.org, client_ip='2a01:c23:9027:b800:34b5:9469:33f9:1ef4', would captcha uri: '/wp-admin/options.php'
30.10.2018 17:01:52 example.org [client 2a01:c23:9000::] rdbm_handle_postscan_block: hostname=example.org, client_ip='2a01:c23:9027:b800:34b5:9469:33f9:1ef4', would captcha uri: '/wp-admin/user-new.php'
30.10.2018 17:06:34 example.org [client 2a01:c23:9000::] rdbm_handle_postscan_block: hostname=example.org, client_ip='2a01:c23:9027:b800:34b5:9469:33f9:1ef4', would captcha uri: '/wp-admin/options.php'
The problem only affects the admin options. Posts and pages can still be created, edited, etc. and updating theme and plugins work fine too.
I'm stuck. I googled for a long time, but unfortunately I can*t find a thread or someone else with the same problem. Anyone here who might be able to help me? I hope I have expressed myself clearly enough.
EDIT: .htaccess
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
