Forbidden error when uploading a file to a specific folder

Nextcloud version 15.0.3:
Operating system and version Ubuntu 16.04:
Apache version 2.4.18:
PHP version 7.0.33:

Is this the first time you’ve seen this error? Yes:

Steps to replicate it:

  1. Login to the web interface with any user (local or LDAP)
  2. Move inside the “Reductor_PDF” folder
  3. Upload a file to the folder (any extension, any size), and gets a Forbidden warning

The output of your Nextcloud log in Admin > Logging:

Nothing to paste

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

root@nextcloudpro:/var/www/nextcloud/config# cat config.php
<?php
$CONFIG = array (
  'passwordsalt' => 'asdasdasdasd',
  'secret' => 'asdasdasd',
  'trusted_domains' =>
  array (
    0 => 'localhost',
    1 => 'asdasd',
    2 => 'asdasd',
    3 => 'nextcloud',
  ),
  'datadirectory' => '/var/ncdata',
  'overwrite.cli.url' => 'https://nextcloud/',
  'dbtype' => 'mysql',
  'version' => '15.0.13.1',
  'dbname' => 'nextcloud_db',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'oc_ncadmin',
  'dbpassword' => 'asdasdasd',
  'installed' => true,
  'instanceid' => 'ocmnpoor4wsx',
  'maintenance' => false,
  'mail_smtpmode' => 'smtp',
  'log_rotate_size' => '10485760',
  'memcache.local' => '\\OC\\Memcache\\Redis',
  'filelocking.enabled' => true,
  'memcache.distributed' => '\\OC\\Memcache\\Redis',
  'trashbin_retention_obligation' => 'D,30',
  'memcache.locking' => '\\OC\\Memcache\\Redis',
  'redis' =>
  array (
    'host' => '/var/run/redis/redis.sock',
    'port' => 0,
    'timeout' => 0,
    'dbindex' => 0,
    'password' => 'asdasdasd',
  ),
  'htaccess.RewriteBase' => '/',
  'loglevel' => 2,
  'updater.release.channel' => 'stable',
  'mail_from_address' => 'nextcloudprod',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_domain' => 'summum.com.uy',
  'mail_smtphost' => 'asdasd',
  'mail_smtpport' => '25',
  'theme' => '',
  'ldapIgnoreNamingRules' => false,
  'ldapProviderFactory' => '\\OCA\\User_LDAP\\LDAPProviderFactory',
);

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

If needed can paste error or access log from apache here.

As breefly descripted above, when trying to upload a file to a specific folder of my NextCloud instalation, we get a litlle Fortibidden message, in other folders there is no problem, the issue manifest with any user that logins (local or LDAP user):

The issue was solved.
The folder with the issue was from an external storage device (SFTP server), I did not know that, the permissions where fixed on the remote folder and error was gone.