Вижу ошибку такого рода
2020/11/21 01:37:32 [error] 80002#80002: *104259 FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught Error: Call to undefined function IPS\mb_internal_encoding() in /home/www/sv.ru-m.org/www/forum/init.php:541
Stack trace:
#0 /home/www/sv.ru-m.org/www/forum/init.php(1370): IPS\IPS::init()
#1 /home/www/sv.ru-m.org/www/forum/index.php(12): require_once('/home/www/sv.ru...')
#2 {main}
thrown in /home/www/sv.ru-m.org/www/forum/init.php on line 541" while reading response header from upstream, client: 185.191.171.24, server: sv.ru-m.org, request: "GET /forum/index.php?%2Flanguage%2F&csrfKey=a7a388015ff6a3274a06d784bb7753e8 HTTP/1.1", upstream: "fastcgi://unix:/run/php/php7.3-fpm.sock:", host: "sv.ru-m.org"