Support intro
Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 12.0.2): 16.0.3
Operating system and version (eg, Ubuntu 17.04): debian 10.0 (docker)
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.38
PHP version (eg, 7.1): 7.3.7
The issue you are facing:
I got an unknown error when I tried to start a new upload during uploading exists.
It is okay to upload multiple files, but when I tried to upload something new while upload is not finish,
the progress bar turned into black and an unknown error appears.
I wonder if it is a bug, but files would be uploaded properly if I just wait.
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
- Upload something.
- Drag another file into nextcloud before previous upload finished.
The output of your Nextcloud log in Admin > Logging:
No new logs during error occured.
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'htaccess.RewriteBase' => '/',
'memcache.local' => '\\OC\\Memcache\\APCu',
'apps_paths' =>
array (
0 =>
array (
'path' => '/var/www/html/apps',
'url' => '/apps',
'writable' => false,
),
1 =>
array (
'path' => '/var/www/html/custom_apps',
'url' => '/custom_apps',
'writable' => true,
),
),
'instanceid' => '***',
'passwordsalt' => '***********',
'secret' => '**********',
'trusted_domains' =>
array (
0 => 'file.****.***',
),
'datadirectory' => '/var/www/html/data',
'dbtype' => 'mysql',
'version' => '16.0.3.0',
'overwrite.cli.url' => 'http://file.****.***',
'dbname' => 'nextcloud',
'dbhost' => 'nextcloud_mysql:3306',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => 'nextcloud',
'dbpassword' => '******',
'installed' => true,
'updater.secret' => '********************',
);
The output of your Apache/nginx/system log in /var/log/____:
172.18.0.2 - - [26/Sep/2019:06:11:37 +0000] "GET /apps/theming/img/core/filetypes/folder-drag-accept.svg?v=1 HTTP/1.1" 200 1331 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:38 +0000] "MKCOL /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898 HTTP/1.1" 201 566 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:40 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/0 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:41 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/10485760 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:42 +0000] "PUT /remote.php/webdav/test/freeswitch1.8%E8%8B%B1%E6%96%87%E7%89%88_compressed.pdf HTTP/1.1" 201 686 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:42 +0000] "GET /index.php/apps/files/ajax/getstoragestats.php HTTP/1.1" 200 1165 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:43 +0000] "PROPFIND /remote.php/dav/files/admin/test/freeswitch1.8%E8%8B%B1%E6%96%87%E7%89%88_compressed.pdf HTTP/1.1" 207 1910 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:44 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/20971520 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:46 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/31457280 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:47 +0000] "GET /ocs/v2.php/apps/notifications/api/v2/notifications HTTP/1.1" 200 718 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:48 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/41943040 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:49 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/52428800 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:51 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/62914560 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:52 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/73400320 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:54 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/83886080 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:55 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/94371840 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:57 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/104857600 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:11:58 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/115343360 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:12:00 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/125829120 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:12:00 +0000] "PUT /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/136314880 HTTP/1.1" 201 599 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:12:01 +0000] "GET /index.php/apps/files/ajax/getstoragestats.php?dir=%2Ftest HTTP/1.1" 200 1163 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:12:00 +0000] "MOVE /remote.php/dav/uploads/admin/web-file-upload-7ba828b97c5730808e85467166628b49-1569478298898/.file HTTP/1.1" 201 708 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"
172.18.0.2 - - [26/Sep/2019:06:12:01 +0000] "PROPFIND /remote.php/dav/files/admin/test/FreeSWITCH%E6%9D%83%E5%A8%81%E6%8C%87%E5%8D%97%2BPDF%E7%94%B5%E5%AD%90%E4%B9%A6%2B%E4%B8%8B%E8%BD%BD%2B%E5%AE%8C%E6%95%B4%E7%89%88.pdf HTTP/1.1" 207 1993 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36"