Comment 2 for bug 1968607

I have tested this with both the DistUpgradeViewGtk3 and DistUpgradeViewText frontends. Using Gtk3, the screen lock prevention code fails, and no failure is reported in the logs. Using the text frontend, the screen lock prevention code works as expected.

I believe the issue is that for the Gtk3 and KDE frontends, the dist-upgrade script is not invoked in a way that preserves the user's environment variables [1], namely `DBUS_SESSION_BUS_ADDRESS` etc. So, the DBus call fails and the failure is not reported because `XDG_SESSION_TYPE` is not set either [2].

[1] https://git.launchpad.net/ubuntu-release-upgrader/tree/do-release-upgrade#n221
[2] https://git.launchpad.net/ubuntu-release-upgrader/tree/DistUpgrade/DistUpgradeController.py#n2079