I have put together a reproducer in a VM:

1. Install Guix system using 1.4.0 installer
  --> Include sshd, openbox

2. Reboot
3. Copy the /run/current-system/configuration.scm out of the VM
4. Adjust the configuration.scm (full file attached)
4.1 Allow NOPASSWD sudo
  (sudoers-file
   (plain-file "sudoers"
               (string-append (plain-file-content %sudoers-specification)
                              (format #f "x ALL = NOPASSWD: ALL~%"))))
4.2 Use %base-services, delete set-xorg-configuration service
4.3 Add dhcp-client-service-type service.
4.4 Authorize your key
  (simple-service
   'extra-authorized-keys guix-service-type
   (guix-extension
    (authorized-keys (list
                      (local-file "/etc/guix/signing-key.pub")))))

5. Manually tweak /etc/sudoers to support NOPASSWD for user x
6. Create machine configuration (full file attached)

7. Guix deploy the machine using b99df83c591104655a6b387817d8f7bb3c50204c
8. Reboot

9. Guix deploy the machine using 1afbf48b250f667ce45de40a6c275e3e42ade67c
  --> See the following error:
  
--8<---------------cut here---------------start------------->8---
building path(s) `/gnu/store/zdknxv3knkkxx52nwfbz120p32z4j2aa-upgrade-shepherd-services.scm'
building path(s) `/gnu/store/x7bzglpc0vvr5ak24k3i33ikq5ph8sfx-remote-exp.scm'
guix deploy: warning: an error occurred while upgrading services on 'localhost':
%exception #<inferior-object #<&service-not-found-error service: system-log>> 
--8<---------------cut here---------------end--------------->8---

A. Reboot
  --> The system does not come up (I gave it ~10 minutes).