Nextcloud user settings not working on web interface

Whenever the user/admin navigates to settings the Internal Server Error message appears.

I looked into the server logs and found out this error code in /nextcloud/data/nextcloud.log

{“reqId”:“LXISMBJ5VQzn1WVMXRe2”,“level”:3,“time”:“2020-05-22T12:56:29+00:00”,“remoteAddr”:“202.51.76.71”,“user”:“admin1”,“app”:“index”,“method”:“GET”,“url”:"/settings/user",“message”:{“Exception”:“Exception”,“Message”:“Class ‘OCP\Config’ not found”,“Code”:0,“Trace”:[{“file”:"/usr/share/nginx/nextcloud/lib/private/AppFramework/App.php",“line”:125,“function”:“dispatch”,“class”:“OC\AppFramework\Http\Dispatcher”,“type”:"->",“args”:[{“class”:“OCA\Settings\Controller\PersonalSettingsController”},“index”]},{“file”:"/usr/share/nginx/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php",“line”:47,“function”:“main”,“class”:“OC\AppFramework\App”,“type”:"::",“args”:[“OCA\Settings\Controller\PersonalSettingsController”,“index”,{“class”:“OC\AppFramework\DependencyInjection\DIContainer”},{“section”:“personal-info”,"_route":“settings.PersonalSettings.index”}]}

How can I solve this issue?

my current conf in /nextcloud/config/config.php

<?php $CONFIG = array ( 'instanceid' => 'iinstance id', 'passwordsalt' => 'password salt', 'secret' => 'sectet key', 'trusted_domains' => array ( 0 => '192.168.10.157', 1 => 'removed for security reason', 2 => 'removed for security reason', ), 'datadirectory' => '/usr/share/nginx/nextcloud/data', 'dbtype' => 'mysql', 'version' => '18.0.4.2', 'overwrite.cli.url' => 'http://192.168.10.157', 'dbname' => 'nextcloud', 'dbhost' => 'localhost', 'dbport' => '', 'dbtableprefix' => 'oc_', 'dbuser' => 'nextclouduser', 'dbpassword' => 'removed for security reason', 'installed' => true, 'mail_smtpmode' => 'smtp', 'mail_smtpsecure' => 'ssl', 'mail_sendmailmode' => 'smtp', 'mail_from_address' => '', 'mail_domain' => '', 'mail_smtpauthtype' => 'LOGIN', 'mail_smtpauth' => 1, 'mail_smtphost' => '', 'mail_smtpport' => '', 'mail_smtpname' => '', 'mail_smtppassword' => '', 'memcache.distributed' => '\\OC\\Memcache\\Redis', 'memcache.local' => '\\OC\\Memcache\\Redis', 'memcache.locking' => '\\OC\\Memcache\\Redis', 'redis' => array ( 'host' => 'localhost', 'port' => 6379, ), 'mysql.utf8mb4' => true, 'maintenance' => false, 'app_install_overwrite' => array ( 0 => 'admin_notifications', 1 => 'keeporsweep', 2 => 'joplin', 3 => 'files_opds', 4 => 'dashboard', 5 => 'activitylog', 6 => 'files_external_gdrive', 7 => 'files_clipboard', 8 => 'defaultlinkopen', 9 => 'documents', ), );