The name "rsync.cz.gentoo.org" resolves into 86.49.49.49 and 171.25.221.40. The former is rsync1.cz.gentoo.org and works fine. The latter hasn't for a long time and isn't listed at https://www.gentoo.org/support/rsync-mirrors/#CZ. There used to be two IPs in the Czech rotation, but one of them went down years ago. It is that one probably.
removed