Comment 42 for bug 1508146

I just had this on 18.04 after applying this upgrade via software-updater. At least I think that's the cause.

Start-Date: 2018-08-13 08:00:02
Commandline: aptdaemon role='role-commit-packages' sender=':1.123'
Install: linux-image-4.15.0-30-generic:amd64 (4.15.0-30.32, automatic), linux-headers-4.15.0-30:amd64 (4.15.0-30.32, automatic), linux-modules-extra-4.15.0-30-generic:amd64 (4.15.0-30.32, automatic), linux-modules-4.15.0-30-generic:amd64 (4.15.0-30.32, automatic), linux-headers-4.15.0-30-generic:amd64 (4.15.0-30.32, automatic)
Upgrade: ca-certificates-java:amd64 (20170930ubuntu1, 20180516ubuntu1~18.04.1), xserver-xorg-input-all:amd64 (1:7.7+19ubuntu7, 1:7.7+19ubuntu7.1), xserver-xorg:amd64 (1:7.7+19ubuntu7, 1:7.7+19ubuntu7.1), libvte-2.91-0:amd64 (0.52.2-1ubuntu1~18.04.1, 0.52.2-1ubuntu1~18.04.2), intel-microcode:amd64 (3.20180425.1~ubuntu0.18.04.1, 3.20180425.1~ubuntu0.18.04.2), linux-headers-generic:amd64 (4.15.0.29.31, 4.15.0.30.32), linux-libc-dev:amd64 (4.15.0-29.31, 4.15.0-30.32), python3-wadllib:amd64 (1.3.2-3, 1.3.2-3ubuntu0.18.04.1), linux-image-generic:amd64 (4.15.0.29.31, 4.15.0.30.32), snapd:amd64 (2.33.1+18.04ubuntu2, 2.34.2+18.04), lshw:amd64 (02.18-0.1ubuntu6, 02.18-0.1ubuntu6.18.04.1), google-chrome-stable:amd64 (68.0.3440.75-1, 68.0.3440.84-1), console-setup-linux:amd64 (1.178ubuntu2.2, 1.178ubuntu2.3), console-setup:amd64 (1.178ubuntu2.2, 1.178ubuntu2.3), amd64-microcode:amd64 (3.20180524.1~ubuntu0.18.04.1, 3.20180524.1~ubuntu0.18.04.2), linux-signed-generic:amd64 (4.15.0.29.31, 4.15.0.30.32), liblxc1:amd64 (3.0.1-0ubuntu1~18.04.1, 3.0.1-0ubuntu1~18.04.2), gir1.2-vte-2.91:amd64 (0.52.2-1ubuntu1~18.04.1, 0.52.2-1ubuntu1~18.04.2), guile-2.0-libs:amd64 (2.0.13+1-5build2, 2.0.13+1-5ubuntu0.1), libmspack0:amd64 (0.6-3, 0.6-3ubuntu0.1), xserver-xorg-video-all:amd64 (1:7.7+19ubuntu7, 1:7.7+19ubuntu7.1), xorg:amd64 (1:7.7+19ubuntu7, 1:7.7+19ubuntu7.1), libmysqlclient20:amd64 (5.7.22-0ubuntu18.04.1, 5.7.23-0ubuntu0.18.04.1), keyboard-configuration:amd64 (1.178ubuntu2.2, 1.178ubuntu2.3), libvte-2.91-common:amd64 (0.52.2-1ubuntu1~18.04.1, 0.52.2-1ubuntu1~18.04.2), x11-common:amd64 (1:7.7+19ubuntu7, 1:7.7+19ubuntu7.1), liblxc-common:amd64 (3.0.1-0ubuntu1~18.04.1, 3.0.1-0ubuntu1~18.04.2), linux-generic:amd64 (4.15.0.29.31, 4.15.0.30.32)
End-Date: 2018-08-13 08:01:14

Solved by rebooting.

    sudo dumpkeys |grep -E '^(\W+)alt(\W+)keycode (105|106) = (Incr|Decr)_Console'

still shows the entries after reboot, but Alt+Left/right doesn't switch vt anymore.