NotFoundError when uploading a shared folder

Nextcloud version (eg, 12.0.2): 16.0.3
Operating system and version (eg, Ubuntu 17.04):
Apache or nginx version (eg, Apache 2.4.25):
PHP version (eg, 7.1):

The issue you are facing:
An error when an external user with the right credential tried to upload files. A file named : “NotFoundError” is found instead in the folder.
The content of this file is :
NotFoundError: Path does not exist

Is this the first time you’ve seen this error? (Y/N): Yes

Steps to replicate it:

  1. Share a folder with upload & editing, password protect (password is a Chinese character), sent link and password to the external user
  2. The user tried to upload files => no success
  3. Found a file in the folder

The output of your Nextcloud log in Admin > Logging:

Couldn't find any related log !

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

  GNU nano 2.7.4                                            File: config.php

  ),
  'filesystem_check_changes' => 0,
  'filelocking.enabled' => 'true',
  'htaccess.RewriteBase' => '/',
  'integrity.check.disabled' => false,
  'knowledgebaseenabled' => false,
  'logfile' => 'PATH TO LOG',
  'loglevel' => 2,
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpauth' => 1,
  'mail_smtpname' => '',
  'mail_smtppassword' => '',
  'mail_smtphost' => '',
  'mail_smtpport' => '465',
  'mail_smtpsecure' => 'ssl',
  'mail_domain' => '',
  'mail_smtpmode' => 'smtp',
  'mail_sendmailmode' => 'smtp',
  'mail_from_address' => '',
  'logtimezone' => 'Europe/Berlin',
  'log_rotate_size' => 104857600,
  'maintenance' => false,
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'memcache.locking' => '\\OC\\Memcache\\Redis',
  'overwriteprotocol' => 'https',
  'preview_max_x' => 1024,
  'preview_max_y' => 768,
  'preview_max_scale_factor' => 1,
  'redis' =>
  array (
    'host' => '/var/run/redis/redis.sock',
    'port' => 0,
    'timeout' => 0.0,
  ),
  'quota_include_external_storage' => false,
  'share_folder' => '/Shares',
  'skeletondirectory' => '',
  'theme' => '',
  'trashbin_retention_obligation' => 'auto, 7',
  'updater.release.channel' => 'stable',
  'has_rebuilt_cache' => true,
);

The output of your Apache/nginx/system log in /var/log/____:

No related error in var/log NGINX
But in /PATH/nextcloud.log

{"reqId":"3LpIqdlZHrRpJrXqiZGD","level":3,"time":"2019-09-02T19:55:13+02:00","remoteAddr":"IP OF THE USER","user":"--","app":"core","method":"DELETE","url":"\/public.php\/webdav\/NotFoundError","message":"unable to rename, destination directory is not writable : \/mnt\/remotenfs\/nc_data\/files_trashbin\/versions","userAgent":"Mozilla\/5.0 (Macintosh; Intel Mac OS X 1$

Just had that problem on Chrome on Windows 10. The reason was an excessive path length - Chrome was actually unable to open the file (also when dragging the same file on the tab strip - nothing happened).
Workaround for me: move the file to the root folder of any drive, then upload.