I am facing the same issue, i am not able to access my wp-admin panel and site is only shwoing home page. To all the other pages, it shows 500error.
Si
PHP Fatal error: Uncaught Error: Call to undefined function trailingslashit() in /home/yessnyex/public_html/wp-includes/plugin.php:755
Stack trace:
#0 /home/yessnyex/public_html/wp-content/plugins/nitropack/constants.php(5): plugin_dir_path(‘/home/yessnyex/…’)
#1 /home/yessnyex/public_html/wp-content/plugins/nitropack/functions.php(6): require_once(‘/home/yessnyex/…’)
#2 /home/yessnyex/public_html/wp-content/advanced-cache.php(14): require_once(‘/home/yessnyex/…’)
#3 /home/yessnyex/public_html/wp-settings.php(95): include(‘/home/yessnyex/…’)
#4 /home/yessnyex/public_html/wp-config.php(91): require_once(‘/home/yessnyex/…’)
#5 /home/yessnyex/public_html/wp-load.php(37): require_once(‘/home/yessnyex/…’)
#6 /home/yessnyex/public_html/wp-blog-header.php(13): require_once(‘/home/yessnyex/…’)
#7 /home/yessnyex/public_html/index.php(17): require(‘/home/yessnyex/…’)
#8 {main}
thrown in /home/yessnyex/public_html/wp-includes/plugin.php on line 755
