PPS: Using ftp2.de.debian.org instead of deb.debian.org there is no such problem.
% host deb.debian.org deb.debian.org is an alias for debian.map.fastlydns.net. debian.map.fastlydns.net has address 151.101.14.132 debian.map.fastlydns.net has IPv6 address 2a04:4e42:3::644 % host ftp2.de.debian.org ftp2.de.debian.org is an alias for ftp.halifax.rwth-aachen.de. ftp.halifax.rwth-aachen.de has address 137.226.34.46 ftp.halifax.rwth-aachen.de has IPv6 address 2a00:8a60:e012:a00::21
