I attempted to download the Gentoo arm64 ISO at about 20:30Z today and was greeted with a 404 error from the bytemark mirror. It seems that Gentoo.org is attempting to serve files from that mirror before the mirror actually has them. I spoke to iamben on IRC about this. He's aware of the issue and asked for me to file a bug.
I think that this affects binary packages too. Checking package index for sys-apps/portage versions: > curl --silent https://mirror.bytemark.co.uk/gentoo/rel eases/amd64/binpackages/17.1/x86-64/Packages | grep 'CPV: sys-apps/por tage' > CPV: sys-apps/portage-3.0.49-r2 > CPV: sys-apps/portage-3.0.59-r1 > CPV: sys-apps/portage-3.0.61-r1 Meanwhile, the .gpkg.tar files are missing. The portage directory doesn't appear in the directory listing. I can find these portage-*.gpkg.tar files on other mirrors.
I think Robin tried to contact them some time ago and didn't get an answer.
I've just emailed them again.