When scandir function is disabled, your newly-installed theme or plugin wouldn't show up. Follow this tutorial, let's solve this issue.

Method 1

vim /usr/local/php/etc/php.ini

Locate disable_functions and delete scandir, then restart PHP

/etc/init.d/php-fpm restart
or
service php-fpm restart

Method 2

sed -i 's/,scandir//g' /usr/local/php/etc/php.ini

Restart PHP

/etc/init.d/php-fpm restart
or
service php-fpm restart