@filisdiez This is for sure not a general FOG problem as we don’t have other users reporting this as far as I know. I can’t replicate this issue either. So I am fairly sure this is something within your environment. Try opening the URL I posted for all the FOG servers you have and see if you always get the proper version printed in the browser.
Looks this could be some kind of HTTP redirect issue. Maybe try this: tail -f /var/log/apache2/*.log (or for CentOS/Redhat: tail -f /var/log/httpd/*_log). Then boot up a client for registration and keep an eye on the logs the moment you see the error on the client screen. Stop the tail log (Ctrl+c) right after you saw the error on the client screen and post a picture of the logs here.