Snapd.core-fixup.service fails

I am creating an Ubuntu-Core 18 image using the ubuntu-image command. After the *.img file is cretaed, I mount it and add custom systemd services (I know this is probably against standard practice).

After unmounting the image, flashing it to a USB device and booting, the snapd.core-fixup.service is called and fails. Consequently Ubuntu core does not fully boot and hangs at:

[ OK ] Started Update UTMP about System Runlevel Changes.

Console-conf does not start as a result and the service file does not exist;

Below is the failed logs from the fixup.service from systemd

user@localhost:~$ sudo systemctl status snapd.core-fixup.service
● snapd.core-fixup.service - Automatically repair incorrect owner/permissions on core devices
   Loaded: loaded (/etc/systemd/system/snapd.core-fixup.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Fri 2019-04-05 18:25:47 UTC; 2min 18s ago
     Docs: man:snap(1)
  Process: 722 ExecStart=/snap/snapd/2567/usr/lib/snapd/snapd.core-fixupdf.sh (code=exited, status=203/EXEC)
 Main PID: 722 (code=exited, status=203/EXEC)

Apr 05 18:25:47 localhost systemd[1]: Starting Automatically repair incorrect owner/permissions on core devices...
Apr 05 18:25:47 localhost systemd[722]: snapd.core-fixup.service: Failed to execute command: No such file or directory
Apr 05 18:25:47 localhost systemd[722]: snapd.core-fixup.service: Failed at step EXEC spawning /snap/snapd/2567/usr/lib/snapd/snapd.core-fixupdf.sh: No such file or directory
Apr 05 18:25:47 localhost systemd[1]: snapd.core-fixup.service: Main process exited, code=exited, status=203/EXEC
Apr 05 18:25:47 localhost systemd[1]: snapd.core-fixup.service: Failed with result 'exit-code'.
Apr 05 18:25:47 localhost systemd[1]: Failed to start Automatically repair incorrect owner/permissions on core devices.

which services do you add … did you try booting the same image without any modification first ?