Last post from me on this topic 🙂
I had a very quick response to my email (sent via the contact form at http://www.upc.ch/en/support/contact/contact/) where someone very helpful asked me to explain the issue and got me to perform a reset of the router part of the box, which I managed to do.
Interestingly (well, I thought so) it was only the http://<horizon-box>/cgi-bin/status.cgi page which was showing blank. If, after I logged in and got the blank screen I went directly to another part of the admin pages, such as directly to http://<horizon-box>/cgi-bin/basic.cgi then that worked. I could then click on anything except the first tab “STATUS” as then I got the blank screen again.
So, as I had a manual workaround to most of the admin functions, support asked me to do a “Factory Default” reset of the router part of the Horizon box in the SYSTEM sub-section. This, surprisingly, didn’t fix the issue and I’ve been informed UPC are going to send me a replacement box.
The service I received has been excellent. Prompt, in Engish, friendly and knowledgeable.