Uncaught ValueError: Unknown format specifier “C”

Uncaught ValueError: Unknown format specifier “C” in /var/www/wp-includes/nav-menu-template.php:285 Stack trace: #0 /var/www/wp-includes/nav-menu-template.php(285): sprintf(‘

Im not really sure how to fix this, I enter safe mode and try to edite the template be it won’t let me. Im not sure if I can delete the template and have my backup just replace it

Thank you for the help