"Gateway timeout" error after upgrading to 5.7.0 or 5.8.0 or 5.9.0 (4315735)

After a successful upgrade of One Identity Safeguard for Privileged Sessions instead of the webUI opening page one can face an nginx generated warning page "Gateway timeout".

The following gets logged into core shell's /var/log/nginx/error.log :

[error] 1169#1169: *303 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 10.12.20.12, server: , request: "GET /index.php?_backend=Main HTTP/1.1", upstream: "fastcgi://unix:/run/php/php-fpm.sock", host: "IPADDR", referrer: "https://IPADDR/"

Log in to core shell of the appliance and edit /etc/nginx/nginx.conf.

Add the following directive after the other fastcgi line:

fastcgi_read_timeout 200s;

and restart nginx via executing:

systemctl restart nginx.service

After that the webUI should be accessible again.