Comment 2 for bug 1654365

I can't see any reason why LightDM could be affecting this - it only sets up the environment and then runs the session. Is this running under Mir? Because /usr/share/lightdm/lightdm.conf.d/52-ubuntu-touch.conf has:

[SeatDefaults]
type=unity
user-session=ubuntu-touch
session-wrapper=/usr/sbin/ubuntu-touch-lightdm-session
unity-compositor-command=/usr/share/ubuntu-touch-session/usc-wrapper

[LightDM]
minimum-vt=1

Which makes /usr/sbin/ubuntu-touch-lightdm-session:

if [ -n "$MIR_SOCKET" ]; then
    exec $@
else
    exec lightdm-session $@
fi

Which suggests under Mir none of the X session code would be run at all?