Oddly never had this problem until today,

Cannot initiate the connection to debian.map.fastly.net:443 (2a04:4e42::644). - Cannot initiate the connection to deb.debian.org:443 (2a04:4e42::644). - connect (101: Network is unreachable)
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Adding these to /etc/sysctl.conf will fix it

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1