Si alguna vez has visto el siguiente error de Nginx; Upstream sent too big header while reading response header from upstream.
Lo puedes resolver en Plesk agregando lo siguiente en Domains > [NOMBRE del SITIO] > Hosting & DNS > Apache & Nginx Settings > Additional nginx directives.
proxy_connect_timeout 360s;
proxy_send_timeout 360s;
proxy_read_timeout 360s;
fastcgi_send_timeout 360s;
fastcgi_read_timeout 360s;
proxy_busy_buffers_size 512k;
proxy_buffers 4 512k;
proxy_buffer_size 256k;
