Comment 20 for bug 1796193

The command do-release-upgrade downloads a tarball of ubuntu-release-upgrader from the release to which you are upgrading e.g. http://archive.ubuntu.com/ubuntu/dists/bionic-proposed/main/dist-upgrader-all/current/bionic.tar.gz. That tarball is then extracted into /tmp/ubuntu-release-upgrader-$TEMP/. To confirm you are getting the right version of the tarball you can check DistUpgradeVersion.py in that folder. It should contain 18.04.33. It looks right to me:

bdmurray@clean-xenial-amd64:~$ cd /tmp/ubuntu-release-upgrader-pn4lfyfj/
bdmurray@clean-xenial-amd64:/tmp/ubuntu-release-upgrader-pn4lfyfj$ cat DistUpgradeVersion.py
VERSION = '18.04.33'