Las páginas en blanco normalmente se muestran a causa de un problema que fue suprimido para evitar mostrar información privada.
Esos errores aunque no se ven en el sitio, casi siempre se almacenan en un registro de errores que podrías ver en tu panel de control del servicio de alojamiento, o consultando con soporte técnico (del servidor) para que te lo faciliten.
Tras habilitar el modo debug como menciona @ThE KuKa deberías poder ver más información del error.
Si tras revisar el registro de errores te encuentras con un error similar al siguiente:
Código: Seleccionar todo
2020/01/16 14:44:30 [error] 414#414: *55 FastCGI sent in stderr: "PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175
PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175
PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175
PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175
PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175
PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175
PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175
PHP message: PHP Notice: iconv(): Wrong charset, conversion from `utf-8' to `utf-16be' is not allowed in /srv/http/localhost/public_html/forum/vendor/patchwork/utf8/src/Patchwork/PHP/Shim/Iconv.php on line 175" while reading response header from upstream, client: xxx.xxx.xxx.xxx, server: localhost, request: "GET /forum/adm/index.php?sid=xxxxxxxxxxxxxxxxxxxxxx HTTP/1.1", upstream: "fastcgi://unix:/run/php-fpm/php-fpm.sock:", host: "xxx.xxx.xxx.xxx", referrer: "http://xxx.xxx.xxx.xxx/"
Asegúrate de tener la extensión/módulo iconv activado. Esto desde los ajustes de PHP, en el panel de administración de tu servidor.