I'm getting the same error building any of my Snap packages on the s390x architecture. For example, the build of OpenJDK on s390x fails:

s390x build of openjdk-beta snap package (openjdk) in ubuntu bionic-updates
https://launchpad.net/~jgneff/openjdk-snap/+snap/openjdk-beta/+build/2183753

The tail end of the build log file shows the following:

Setting up apparmor (2.12-4ubuntu5.3) ...
Created symlink /etc/systemd/system/sysinit.target.wants/apparmor.service → /lib/systemd/system/apparmor.service.
find: ‘’: No such file or directory
Warning from stdin (line 1): /sbin/apparmor_parser: cannot use or update cache, disable, or force-complain via stdin
Warning failed to create cache: (null)
Setting up dbus-user-session (1.12.2-1ubuntu1.4) ...
Setting up libgssapi-krb5-2:s390x (1.16-2ubuntu0.4) ...
Setting up libgssapi3-heimdal:s390x (7.5.0+dfsg-1ubuntu0.4) ...
Setting up openssh-client (1:7.6p1-4ubuntu0.7) ...
Setting up snapd (2.58+18.04.1) ...
Created symlink /etc/systemd/system/multi-user.target.wants/snapd.aa-prompt-listener.service → /lib/systemd/system/snapd.aa-prompt-listener.service.
Created symlink /etc/systemd/system/multi-user.target.wants/snapd.apparmor.service → /lib/systemd/system/snapd.apparmor.service.
Created symlink /etc/systemd/system/multi-user.target.wants/snapd.autoimport.service → /lib/systemd/system/snapd.autoimport.service.
Created symlink /etc/systemd/system/multi-user.target.wants/snapd.core-fixup.service → /lib/systemd/system/snapd.core-fixup.service.
Created symlink /etc/systemd/system/multi-user.target.wants/snapd.recovery-chooser-trigger.service → /lib/systemd/system/snapd.recovery-chooser-trigger.service.
Created symlink /etc/systemd/system/multi-user.target.wants/snapd.seeded.service → /lib/systemd/system/snapd.seeded.service.
Created symlink /etc/systemd/system/cloud-final.service.wants/snapd.seeded.service → /lib/systemd/system/snapd.seeded.service.
Created symlink /etc/systemd/system/multi-user.target.wants/snapd.service → /lib/systemd/system/snapd.service.
Created symlink /etc/systemd/system/timers.target.wants/snapd.snap-repair.timer → /lib/systemd/system/snapd.snap-repair.timer.
Created symlink /etc/systemd/system/sockets.target.wants/snapd.socket → /lib/systemd/system/snapd.socket.
Created symlink /etc/systemd/system/final.target.wants/snapd.system-shutdown.service → /lib/systemd/system/snapd.system-shutdown.service.
Setting up libldap-2.4-2:s390x (2.4.45+dfsg-1ubuntu1.11) ...
Setting up libcurl3-gnutls:s390x (7.58.0-2ubuntu3.24) ...
Setting up git (1:2.17.1-1ubuntu0.18) ...
Processing triggers for systemd (237-3ubuntu10.57) ...
Processing triggers for libc-bin (2.27-3ubuntu1.6) ...
error: cannot communicate with server: Post http://localhost/v2/snaps/snapcraft: dial unix /run/snapd.socket: connect: no such file or directory
Install failed
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/lpbuildd/target/build_snap.py", line 259, in run
    self.install()
  File "/usr/lib/python3/dist-packages/lpbuildd/target/build_snap.py", line 165, in install
    self.backend.run(
  File "/usr/lib/python3/dist-packages/lpbuildd/target/lxd.py", line 716, in run
    subprocess.check_call(cmd, **kwargs)
  File "/usr/lib/python3.10/subprocess.py", line 369, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['lxc', 'exec', 'lp-bionic-s390x', '--', 'linux64', 'snap', 'install', '--classic', '--channel=latest/stable', 'snapcraft']' returned non-zero exit status 1.
Revoking proxy token...
RUN: /usr/share/launchpad-buildd/bin/in-target scan-for-processes --backend=lxd --series=bionic --arch=s390x SNAPBUILD-2183753
Scanning for processes to kill in build SNAPBUILD-2183753