@aperiamb Try disabling the firewall as a test (and leave it disabled while we try to figure out what is the cause here so we don’t have to go back and forth)

I personally suspect PHP-FPM to be the real culprit, a PHP error would produce a blank page on index.php (as opposed to an apache error page which will give an error code)

What’s the output of

tail -50 /var/log/php-fpm/www-error.log

and

tail -50 /var/log/php-fpm/error.log