On top of all the other problems of the last week, my ISP had a network outage caused by a configuration error somewhere in their setup. Specifically, they have a circular fiber ring which somehow contrived to recycle traffic leading to a slow but inevitable meltdown of capacity.
As a result the server has been unreachable since roughly 01:00 CEST (GMT+1/UTC+2) up until around 23:00 CEST (~3 hours ago).
On behalf of my ISP, sorry for the inconvenience. At least it wasn’t me or my hardware this time :)