Error during cron job execution (AutoLoadNotAllowedException)

During the execution of the cron jobs, this error keeps popping up. It appears to have something to do with removing orphaned files. In the logging section of the admin console, there is this:

Error while running background job (OCP\AutoloadNotAllowedException): Autoload path not allowed: /var/www/xxxx.nl/public_html/nextcloud/apps/ojsxc/settings/admin.php
OC\Settings\RemoveOrphaned ):
/var/www/xxxx.nl/public_html/nextcloud/lib/autoloader.php - line 158: OC\Autoloader->isValidPath('/var/www/xxxx....')
[internal function] OC\Autoloader->load('OCA\\OJSXC\\Setti...')
[internal function] spl_autoload_call('OCA\\OJSXC\\Setti...')
/var/www/xxxx.nl/public_html/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php - line 94: ReflectionClass->__construct('OCA\\OJSXC\\Setti...')
/var/www/xxxx.nl/public_html/nextcloud/lib/private/AppFramework/Utility/SimpleContainer.php - line 117: OC\AppFramework\Utility\SimpleContainer->resolve('OCA\\OJSXC\\Setti...')
/var/www/xxxx.nl/public_html/nextcloud/lib/private/ServerContainer.php - line 132: OC\AppFramework\Utility\SimpleContainer->query('OCA\\OJSXC\\Setti...')
/var/www/xxxx.nl/public_html/nextcloud/lib/private/Settings/Manager.php - line 138: OC\ServerContainer->query('OCA\\OJSXC\\Setti...')
/var/www/xxxx.nl/public_html/nextcloud/lib/private/Settings/RemoveOrphaned.php - line 85: OC\Settings\Manager->checkForOrphanedClassNames()
/var/www/xxxx.nl/public_html/nextcloud/lib/private/BackgroundJob/Job.php - line 59: OC\Settings\RemoveOrphaned->run(NULL)
/var/www/xxxx.nl/public_html/nextcloud/lib/private/BackgroundJob/TimedJob.php - line 54: OC\BackgroundJob\Job->execute(Object(OC\BackgroundJob\JobList), Object(OC\Log))
/var/www/xxxx.nl/public_html/nextcloud/lib/private/Settings/RemoveOrphaned.php - line 69: OC\BackgroundJob\TimedJob->execute(Object(OC\BackgroundJob\JobList), Object(OC\Log))
/var/www/xxxx.nl/public_html/nextcloud/cron.php - line 124: OC\Settings\RemoveOrphaned->execute(Object(OC\BackgroundJob\JobList), Object(OC\Log))
{main}

I don’t really have a clue what’s causing this error and would appreciate some pointers where to look.

Nextcloud version: 12.0.0
Operating system and version: Ubuntu 16.04
Apache version: Apache/2.4.18
PHP version: 7.0.18-0ubuntu0.16.04.1
Is this the first time you’ve seen this error: Yes

Can you reliably replicate it? (If so, please outline steps):
Yes, it happens every 15 minutes at cron execution.

The issue you are facing:
No specific issues but I am wondering what the cause is.

Config.php:

<?php
$CONFIG = array (
  'instanceid' => '-------',
  'passwordsalt' => '----------',
  'secret' => '--------',
  'trusted_domains' => 
  array (
    0 => 'www.xxxx.nl',
    1 => '1.2.3.4',
    2 => 'xxxx.nl',
  ),
  'datadirectory' => '/home/nextcloud',
  'overwrite.cli.url' => 'https://www.xxxx.nl/nextcloud',
  'dbtype' => 'mysql',
  'version' => '12.0.0.29',
  'dbname' => '-----',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => '------',
  'dbpassword' => '--------',
  'logtimezone' => 'UTC',
  'installed' => true,
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'memcache.locking' => '\\OC\\Memcache\\Redis',
  'filelocking.enabled' => 'true',
  'redis' => 
  array (
    'host' => '/var/run/redis/redis.sock',
    'port' => 0,
    'timeout' => 0.0,
  ),
  'htaccess.RewriteBase' => '/nextcloud',
  'updater.release.channel' => 'stable',
  'maintenance' => false,
  'theme' => '',
  'logfile' => '/var/log/nextcloud.log',
  'loglevel' => 2,
  'log_rotate_size' => 10485760,
);

The output of your Apache/nginx/system log in /var/log/____:
Nothing relevant to this error

Any help would be appreciated!

The problem described above and despite searching on my end, I have not been able to find a useful clue.
Anyone an idea? Reactions would be appreciated.

Problem still exists

Error while running background job (OCP\AutoloadNotAllowedException): Autoload path not allowed: /var/www-nextcloud/apps/ojsxc/settings/personal.php`

Nextcloud version : 13.0.4
Operating system and version : Ubuntu 16.04.4
Apache version : Apache/2.4.18 (Ubuntu) OpenSSL/1.0.2g mod_wsgi/4.3.0 Python/2.7.12
PHP version : PHP 7.0.30-0ubuntu0.16.04.1