The server OS has been upgraded to the latest version, and to take advantage of the updates 100%, I restarted the server. The issue was that the server, on reboot, unexpectedly prompted for a disk scan – which shows up before the remote connection is enabled. Since the server is hosted at a provider, the server was unreachable to me since then. I contacted the provider immediately, but until they got someone to go to the server, check it, ask me for the password needed to do the disk scan, until I had time to reply, and then until they again got there to start the disk scan, some hours passed away.
So far so good, just some downtime. There should be only minimal loss of data/changes for people who have been working on the server until the last minute.
Tomorrow I will test the 1.5 setup and see if we can upgrade already with the minimum configuration necessary. Maybe some functions will have to wait until the plugins are updated, but I will try to get the main functionalities running on 1.5 ASAP.