Bug#867402: Debootstrap Error Couldn't retrieve dists/stretch/main/binary-amd64/Packages

[jg@wn.de]

Additional information to reproduce the problem:

1) stretch install is started with pxelinux with this parameters:

        LABEL   v
        MENU LABEL (^v) vga console amd64
        kernel linux/debian/stretch/9.0/amd64/linux
        append initrd=linux/debian/stretch/9.0/amd64/initrd.gz patchlevel=20170618T160104Z BOOT_DEBUG=2 DEBCONF_DEBUG=5 log_host=192.168.120.22 log_port=554 ipv6.disable=1 language=en country=DE locale=en_GB.UTF
-8 keymap=de url=http://preseed.company.tld/linux/debian/preseed/stretch/x.cfg --- ipv6.disable=1


2) the preseed file x.cfg looks like this

# time/zone
d-i		time/zone		select	Europe/Berlin
tzsetup-udeb	time/zone		select	Europe/Berlin
tzsetup-udeb	tzsetup/country/DE	select	Europe/Berlin

# Participate in the package usage survey?
popularity-contest popularity-contest/participate boolean false

# skip creation of a normal user account.
d-i passwd/make-user boolean false

# lang & keyboard
d-i debian-installer/language string en
d-i debian-installer/country string DE
d-i debian-installer/locale string en_GB.UTF-8  
d-i localechooser/supported-locales multiselect en_US.UTF-8, de_DE.UTF-8
d-i keyboard-configuration/xkb-keymap select de

### Mirror settings
d-i mirror/protocol string http
d-i mirror/country string manual
d-i mirror/http/hostname string snapshot.debian.org
d-i mirror/http/directory string /archive/debian/20170618T160104Z
d-i mirror/http/proxy string http://proxy.company.tld:8000

3) The syslog output of the installer with DEBCONF_DEBUG=5 kernel command line
   Here are the last lines just before failing

Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; --> METAGET base-installer/debootstrap/error/couldntdl description
Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; <-- 0 Debootstrap Error
Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; --> SUBST base-installer/debootstrap/error/couldntdl SUBST0 dists/stretch/main/binary-amd64/Packages
Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; Adding [SUBST0] -> [dists/stretch/main/binary-amd64/Packages]
Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; <-- 0
Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; --> INPUT critical base-installer/debootstrap/error/couldntdl
Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; <-- 0 question will be asked
Jul  6 14:21:44;debian-stretch.company.tld;user.debug;debconf:; --> GO

The complete syslog output can be found here https://cloud.aschendorff.de/s/QrEBjzW8txqHFwN