As was announced earlier, the linux login (ssh) servers (lilo5.science.ru.nl and lilo6.science.ru.nl) have swapped their nicknames, which makes Ubuntu 18.04 the standard instead of Ubuntu 16.04. The name lilo.science.ru.nl now refers to lilo6.science.ru.nl and stitch.science.ru.nl now refers to lilo5.science.ru.nl. If you get complaints about changed finger-prints, you know why. See also the page about servers.