My broadband connection dropped out for a few hours last night (red light on router). It did reconnect, but when it did so I found that I could no longer access a couple of the websites I have on Speed dial. They were http, not https, but either displayed 400 Bad request or 401 Unauthorized errors and demanded logins. When I tried to access the sites by typing in the URL directly, or by locating the site via a Google search, same problem. Switching from Opera to the stock Android browser on my tablet made no difference. But I then found that searching for the site and opening it using DuckDuckGo instead of Google did allow me back in. So if anyone else experiences this kind of problem after a broadband outage, try accessing the websites via a different search engine to your usual one.
This seems to have been specific to the tablet I was using when the broadband disconnection occurred, I could get into the affected websites from my mobile.