I am getting the same issue, same error. Crashes once I reach the progress screen of 18.04 installation.

Syslog report:

......


Apr 28 20:26:54 ubuntu localechooser: info: Set debian-installer/locale = 'en_CA.UTF-8'
Apr 28 20:26:54 ubuntu localechooser: info: System locale (debian-installer/locale) = 'en_CA.UTF-8'
Apr 28 20:26:54 ubuntu ubiquity: /usr/lib/ubiquity/localechooser/localechooser: 910: [: C.UTF-8: unexpected operator
Apr 28 20:26:54 ubuntu ubiquity[3103]: debconffilter_done: ubi-timezone (current: ubi-timezone)
Apr 28 20:26:54 ubuntu ubiquity[3103]: Step_before = stepLocation
Apr 28 20:26:54 ubuntu partman: mke2fs 1.44.1 (24-Mar-2018)
Apr 28 20:26:54 ubuntu ubiquity[3103]: switched to page usersetup
Apr 28 20:26:54 ubuntu clear_partitions: Considering /home,/dev/nvme0n1p6.
Apr 28 20:26:54 ubuntu kernel: [  100.161039] EXT4-fs (nvme0n1p6): mounted filesystem with ordered data mode. Opts: (null)
Apr 28 20:26:54 ubuntu kernel: [  100.278116] EXT4-fs (nvme0n1p7): mounted filesystem with ordered data mode. Opts: errors=remount-ro
Apr 28 20:26:54 ubuntu kernel: [  100.296127] EXT4-fs (nvme0n1p6): mounted filesystem with ordered data mode. Opts: (null)
Apr 28 20:26:55 ubuntu ubiquity: File descriptor 3 (pipe:[67210]) leaked on pvs invocation. Parent PID 18458: /bin/sh
Apr 28 20:26:55 ubuntu ubiquity[3103]: debconffilter_done: ubiquity.components.partman_commit (current: ubi-usersetup)
Apr 28 20:26:55 ubuntu /install.py: keeping packages due to preseeding: icedtea6-plugin openoffice.org
Apr 28 20:26:55 ubuntu /install.py: keeping language packs for: en_US.UTF-8
Apr 28 20:26:56 ubuntu ubiquity: W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/bionic/InRelease  Could not resolve 'archive.ubuntu.com'
Apr 28 20:26:56 ubuntu ubiquity: W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/bionic-security/InRelease  Could not resolve 'security.ubuntu.com'
Apr 28 20:26:56 ubuntu ubiquity: W: Failed to fetch http://archive.ubuntu.com/ubuntu/dists/bionic-updates/InRelease  Could not resolve 'archive.ubuntu.com'
Apr 28 20:26:56 ubuntu ubiquity: W: Some index files failed to download. They have been ignored, or old ones used instead.
Apr 28 20:26:56 ubuntu ubiquity: W: --force-yes is deprecated, use one of the options starting with --allow instead.
Apr 28 20:27:13 ubuntu ubiquity[3103]: debconffilter_done: ubi-usersetup (current: ubi-usersetup)
Apr 28 20:27:13 ubuntu ubiquity[3103]: Step_before = stepUserInfo
Apr 28 20:27:14 ubuntu kernel: [  119.884166] do_trap: 26 callbacks suppressed
Apr 28 20:27:14 ubuntu kernel: [  119.884168] traps: ubiquity[3103] trap int3 ip:7ff0a1502c41 sp:7ffe0681d810 error:0 in libglib-2.0.so.0.5600.1[7ff0a14b1000+113000]
Apr 28 20:27:25 ubuntu /install.py: Exception during installation:
Apr 28 20:27:25 ubuntu /install.py: Traceback (most recent call last):
Apr 28 20:27:25 ubuntu /install.py:   File "/usr/share/ubiquity/install.py", line 765, in <module>
Apr 28 20:27:25 ubuntu /install.py:     install.run()
Apr 28 20:27:25 ubuntu /install.py:   File "/usr/share/ubiquity/install.py", line 135, in run
Apr 28 20:27:25 ubuntu /install.py:     self.copy_all()
Apr 28 20:27:25 ubuntu /install.py:   File "/usr/share/ubiquity/install.py", line 513, in copy_all
Apr 28 20:27:25 ubuntu /install.py:     self.db.progress('SET', 10 + copy_progress)
Apr 28 20:27:25 ubuntu /install.py:   File "/usr/lib/python3/dist-packages/debconf.py", line 83, in <lambda>
Apr 28 20:27:25 ubuntu /install.py:     lambda *args, **kw: self.command(command, *args, **kw))
Apr 28 20:27:25 ubuntu /install.py:   File "/usr/lib/python3/dist-packages/debconf.py", line 104, in command
Apr 28 20:27:25 ubuntu /install.py:     status = int(status)
Apr 28 20:27:25 ubuntu /install.py: ValueError: invalid literal for int() with base 10: ''
Apr 28 20:27:25 ubuntu /install.py: 
Apr 28 20:27:25 ubuntu nautilus-autostart.desktop[2103]: Trace/breakpoint trap (core dumped)
Apr 28 20:27:31 ubuntu dbus-daemon[1666]: [session uid=999 pid=1666] Activating via systemd: service name='org.gnome.Terminal' unit='gnome-terminal-server.service' requested by ':1.81' (uid=999 pid=18835 comm="/usr/bin/gnome-terminal.real " label="unconfined")
Apr 28 20:27:31 ubuntu systemd[1622]: Starting GNOME Terminal Server...
Apr 28 20:27:31 ubuntu dbus-daemon[1666]: [session uid=999 pid=1666] Successfully activated service 'org.gnome.Terminal'
Apr 28 20:27:31 ubuntu systemd[1622]: Started GNOME Terminal Server.