Oh this issue.
This is when there is a line fault, the router drops the Internet connection. It then brings up a page saying "your connection has dropped." iPhones, iPads etc will display this page in the same way as they display a bt wifi hotspot page, that is they will display it and then switch onto 3G or 4G when the user goes off the page, as the iPhone etc detects that the broadband has dropped out.
Users then report that their wifi is dropping - no the wifi is fine but the phone / iPad etc is not using it as the underlying broadband connection has dropped. So it's gone onto 3G or 4G after displaying the "your connection has dropped" page on one of the devices.
It is not a router fault or a wifi dropping issue, it is their actual broadband connection dropping and is usually caused by not using the master phone socket, having poor internal wiring or an external line fault. It is not something sky can just "fix" with a router update it requires the user to either move their router to the master socket or in some cases a bt engineer visit to correct the line fault.