Upload through the WebInterface does not work

Nextcloud version 12.0.3:
Operating system and version Debian 9.1:
nginx version __:
PHP version 7.0.19:
Is this the first time you’ve seen this error?: Yes

Can you reliably replicate it? (If so, please outline steps):

The issue you are facing:
I have Installed a fresh Installation of Nextcloud on a Debian / Nginx php7-fpm with ISPConfig 3.1 Machine. everything works fine but i cant Upload any files. Nextcloud told me everytime: Theres not enough space for the files.
But my Settings allow 20G (for testing purpose)
By the way i CAN Upload anything with the nextcloud desktop client or android client. only WebInterface doesnt work.
And i can delet everything through the WebInterface

The output of your Nextcloud log in Admin > Logging:
Zend OPcache can’t be temporary enabled (it may be only disabled till the end of request) at Unknown#0

internet_connection_check GuzzleHttp\Exception\RequestException: cURL error 18: transfer closed with 26500 bytes remaining to read

Nginx doesnt say any error or something in the log files
If you have some more questions feel free to ask

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

$CONFIG = array (
‘instanceid’ => ‘id?’,
‘passwordsalt’ => ‘salt’,
‘secret’ => ‘skey’,
‘trusted_domains’ =>
array (
0 => ‘cloud.domain.com’,
),
‘datadirectory’ => ‘/var/www/clients/client1/web2/private/NXTData’,
‘overwrite.cli.url’ => ‘http://cloud.domain.com’,
‘dbtype’ => ‘mysql’,
‘version’ => ‘12.0.3.3’,
‘dbname’ => ‘’,
‘dbhost’ => ‘localhost’,
‘dbport’ => ‘’,
‘dbtableprefix’ => ‘oc_’,
‘mysql.utf8mb4’ => true,
‘dbuser’ => ‘’,
‘dbpassword’ => ‘’,
‘installed’ => true,
);

my nginx vhost:

add_header Strict-Transport-Security “max-age=15768000; includeSubDomains; preload;”;
add_header X-Content-Type-Options nosniff;
add_header X-Frame-Options “SAMEORIGIN”;
add_header X-XSS-Protection “1; mode=block”;
add_header X-Robots-Tag none;
add_header X-Download-Options noopen;
add_header X-Permitted-Cross-Domain-Policies none;
location = /robots.txt {
allow all;
log_not_found off;
access_log off;
}

    location ~ \.php$ {
        try_files /642550b4c0a90e4013edb28d4df438a0.htm @php;
    }

# The following 2 rules are only needed for the user_webfinger app.
# Uncomment it if you're planning to use this app.
#rewrite ^/.well-known/host-meta /public.php?service=host-meta last;
#rewrite ^/.well-known/host-meta.json /public.php?service=host-meta-json last;

location = /.well-known/carddav {
    return 301 $scheme://$host/remote.php/dav;
}

location = /.well-known/caldav {
    return 301 $scheme://$host/remote.php/dav;
}

location /.well-known/acme-challenge { }
# set max upload size
client_max_body_size 20G;
fastcgi_buffers 64 4K;
# Disable gzip to avoid the removal of the ETag header
gzip off;
# Uncomment if your server is build with the ngx_pagespeed module
# This module is currently not supported.
# pagespeed off;
error_page 403 /core/templates/403.php;
error_page 404 /core/templates/404.php;
location / {
    rewrite ^ /index.php$uri;
}
location ~ ^/(?:build|tests|config|lib|3rdparty|templates|data)/ {
    return 404;
}
location ~ ^/(?:\.|autotest|occ|issue|indie|db_|console) {
    return 404;
}
location ~ ^(.+?\.php)(/.*)?$ {
                    try_files $1 =404;
                    include fastcgi_params;
                    fastcgi_param SCRIPT_FILENAME $document_root$1;
                    fastcgi_param PATH_INFO $2;
                    fastcgi_param HTTPS $https;
                    {FASTCGIPASS}
                    fastcgi_intercept_errors on;
                    fastcgi_index index.php;
                    fastcgi_buffers 64 64K;
                    fastcgi_buffer_size 256k;
                    fastcgi_param modHeadersAvailable true;
                    fastcgi_read_timeout 7200; 
    }
location @php2 {
                    fastcgi_split_path_info ^((?U).+\.php)(/?.+)$;
                    include fastcgi_params;
                    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                    fastcgi_param PATH_INFO $fastcgi_path_info;
                    fastcgi_param HTTPS $https;
                    {FASTCGIPASS}
                    fastcgi_intercept_errors on;
                    fastcgi_index index.php;
                    fastcgi_buffers 64 64K;
                    fastcgi_buffer_size 256k;
                    fastcgi_param modHeadersAvailable true;
                    fastcgi_read_timeout 7200; 
    }
location ~ ^/(?:index|remote|public|cron|core/ajax/update|status|ocs/v[12]|updater/.+|ocs-provider/.+|core/templates/40[34])\.php(?:$|/) {
    fastcgi_split_path_info ^(.+\.php)(/.*)$;
    include fastcgi_params;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_param PATH_INFO $fastcgi_path_info;
    fastcgi_param HTTPS on;
    fastcgi_param modHeadersAvailable true; #Avoid sending the security headers twice
    fastcgi_param front_controller_active true;
    #fastcgi_pass php-handler;

#fastcgi_pass unix:/var/run/hhvm/hhvm.sock;
{FASTCGIPASS}
fastcgi_intercept_errors on;
fastcgi_request_buffering off;
}
location ~ ^/(?:updater|ocs-provider)(?:$|/) {
try_files $uri/ =404;
index index.php;
}
# Adding the cache control header for js and css files
# Make sure it is BELOW the PHP block
location ~* .(?:css|js)$ {
try_files $uri /index.php$uri$is_args$args;
add_header Cache-Control “public, max-age=7200”;
# Add headers to serve security related headers (It is intended to have those duplicated to the ones above)
# Before enabling Strict-Transport-Security headers please read into this topic first.
# add_header Strict-Transport-Security “max-age=15768000; includeSubDomains; preload;”;
add_header X-Content-Type-Options nosniff;
add_header X-Frame-Options “SAMEORIGIN”;
add_header X-XSS-Protection “1; mode=block”;
add_header X-Robots-Tag none;
add_header X-Download-Options noopen;
add_header X-Permitted-Cross-Domain-Policies none;
# Optional: Don’t log access to assets
access_log off;
}
location ~* .(?:svg|gif|png|html|ttf|woff|ico|jpg|jpeg)$ {
try_files $uri /index.php$uri$is_args$args;
# Optional: Don’t log access to other assets
access_log off;
}
location = /data/htaccesstest.txt {
allow all;
log_not_found off;
access_log off;
}

OK, i tried something:
I have create a 0 kb big file… and tried to upload this file…
it works perfectly.

The i tried a biger file <1 kb + = error

Here is the log file for this:

77.21.32.94 - - [06/Oct/2017:20:09:36 +0200] “PUT /remote.php/webdav/Neues%20Textdokument%20(3).txt HTTP/1.1” 201 0 “-” "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36"
77.21.32.94 - - [06/Oct/2017:20:09:36 +0200] “PROPFIND /remote.php/webdav/Neues%20Textdokument%20(3).txt HTTP/1.1” 207 902 “-” "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36"
77.21.32.94 - Shinon.Kagura [06/Oct/2017:20:09:50 +0200] “PROPFIND /remote.php/dav/files/Shinon.Kagura/ HTTP/1.1” 207 513 “-” "Mozilla/5.0 (Windows) mirall/2.3.2 (build 1) (Nextcloud)"
77.21.32.94 - Shinon.Kagura [06/Oct/2017:20:09:50 +0200] “GET /ocs/v2.php/apps/notifications/api/v1/notifications?format=json HTTP/1.1” 200 1259 “-” "Mozilla/5.0 (Windows) mirall/2.3.2 (build 1) (Nextcloud)"
77.21.32.94 - Shinon.Kagura [06/Oct/2017:20:09:50 +0200] “PROPFIND /remote.php/dav/files/Shinon.Kagura/ HTTP/1.1” 207 3888 “-” "Mozilla/5.0 (Windows) mirall/2.3.2 (build 1) (Nextcloud)"
77.21.32.94 - - [06/Oct/2017:20:09:51 +0200] “GET /ocs/v2.php/apps/notifications/api/v2/notifications HTTP/1.1” 200 1495 “-” "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36"
77.21.32.94 - Shinon.Kagura [06/Oct/2017:20:09:51 +0200] “GET /remote.php/dav/files/Shinon.Kagura/Neues%20Textdokument%20(3).txt HTTP/1.1” 200 5 “-” "Mozilla/5.0 (Windows) mirall/2.3.2 (build 1) (Nextcloud)"
77.21.32.94 - - [06/Oct/2017:20:10:21 +0200] “GET /ocs/v2.php/apps/notifications/api/v2/notifications HTTP/1.1” 200 1495 “-” "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36"
77.21.32.94 - Shinon.Kagura [06/Oct/2017:20:10:26 +0200] “PROPFIND /remote.php/dav/files/Shinon.Kagura/ HTTP/1.1” 207 533 “-” “Mozilla/5.0 (Windows) mirall/2.3.2 (build 1) (Nextcloud)”

My Max Size for Upload is 20 GB (for testing purpose)