Guru has always been a dynamic system, with regular updates being pushed out to our customers. This creates a better experience for customers but it means that we occasionally need to patch servers to apply these updates.
In addition, due to the high security needs, we keep an aggressive operating system security patching schedule.
Rebooting the server or applying a new patch takes just a minute or two. If someone previously attempted to visit the site during this window (typically out of hours) they previously encountered an uninformative, basic error screen.
As of the latest version, a more informative error page has been added, which will automatically keep trying to refresh until the site comes back up. This should limit confusion and the number of support requests which could have arisen from the previous page.