Upgrade to Version 4 fails

[jfb]

Admin GUI > settings > teleporter. Export the file to your computer somewhere (not on the Pi). Then you'll have it later. Same screen to import, on the right side. The teleporter also saves a few of your configuration files in case you need to refer to them later.

[Mcat12]

Your pihole -r output only gets to installing packages, and seems to fail there. Have you tried manually installing the packages it marked for installation?

[i] Checking for dns-root-data (will be installed)
[i] Checking for resolvconf (will be installed)

[Floriano]

Hey again,
it seems to me that I have completely messed it up.

I made a backup via teleport
I run sudo pihole uninstall

changed in the router the DHCP and DNS so that DHCP is provided by the router and DNS is 8.8.8.8 and 2nd for provider specific

after reboot of system (pi zero w, with stretch) i changed the nameserver from 127.0.0.1 to 8.8.8.8
and did
sudo apt-get update
OK:1 http://raspbian.raspberrypi.org/raspbian stretch InRelease
OK:2 http://archive.raspberrypi.org/debian stretch InRelease
Paketlisten werden gelesen... Fertig

and

sudo apt-get upgrade
Paketlisten werden gelesen... Fertig
Abhängigkeitsbaum wird aufgebaut.
Statusinformationen werden eingelesen.... Fertig
Paketaktualisierung (Upgrade) wird berechnet... Fertig
0 aktualisiert, 0 neu installiert, 0 zu entfernen und 0 nicht aktualisiert.

now I tried to install pi-hole with

sudo curl -sSL https://install.pi-hole.net | bash

[✗] Root user check
[i] Script called with non-root privileges
[i] The Pi-hole requires elevated privileges to install and run
[i] Please check the installer for any concerns regarding this requirement
[i] Make sure to download this script from a trusted source

[✓] Sudo utility check

[✓] Root user check

    .;;,.
    .ccccc:,.
     :cccclll:.      ..,,
      :ccccclll.   ;ooodc
       'ccll:;ll .oooodc
         .;cll.;;looo:.
             .. ','.
            .',,,,,,'.
          .',,,,,,,,,,.
        .',,,,,,,,,,,,....
      ....''',,,,,,,'.......
    .........  ....  .........
    ..........      ..........
    ..........      ..........
    .........  ....  .........
      ........,,,,,,,'......
        ....',,,,,,,,,,,,.
           .',,,,,,,,,'.
            .',,,,,,'.
              ..'''.

[i] Existing PHP installation detected : PHP version 7.0.27-0+deb9u1
[✓] Disk space check

[✓] Update local cache of available packages

[✓] Checking apt-get for upgraded packages... up to date!

[i] Installer Dependency checks...
[i] Checking for apt-utils (will be installed)
[i] Checking for dialog (will be installed)
[✓] Checking for debconf
[✓] Checking for dhcpcd5
[✓] Checking for git
[✓] Checking for iproute2
[✓] Checking for whiptail

Here it stops, install is not successful, no further errors.
Any ideas I could follow to find my bug?

[jfb]

It looks like you only have a few other applications running on the Pi. If I were in your position, I would format the SD card, reinstall a clean version of Stretch (or Stretch Lite), then install Pi-Hole.